This is stated in the Vedānta-sūtra (janmādy asya yataḥ). The source of birth of the cosmic manifestation, or mahat-tattva, is the Personality of Godhead. This is confirmed throughout Śrīmad-Bhāgavatam and the Bhagavad-gītā. In the Bhagavad-gītā (10.8) the Lord says, ahaṁ sarvasya prabhavaḥ: "I am the fountainhead of all emanations." The material cosmos, being temporary, is sometimes manifest and sometimes unmanifest, but its energy emanates from the Supreme Absolute Lord. Before the creation there was neither cause nor effect, but the Supreme Personality of Godhead existed with His full opulence and energy.
The words paścād aham indicate that the Lord exists after the dissolution of the cosmic manifestation. When the material world is dissolved, the Lord still exists personally in the Vaikuṇṭhas. During the creation the Lord also exists as He is in the Vaikuṇṭhas, and He also exists as the Supersoul within the material universes. This is confirmed in the Brahma-saṁhitā (5.37). Goloka eva nivasati: although He is perfectly and eternally present in Goloka Vṛndāvana in Vaikuṇṭha, He is nevertheless all-pervading (akhilātma-bhūtaḥ). The all-pervading feature of the Lord is called the Supersoul. In the Bhagavad-gītā it is said, ahaṁ kṛtsnasya jagataḥ prabhavaḥ: the cosmic manifestation is a display of the energy of the Supreme Lord.
(Sri Caitanya Caritamrta----1:1:53-----purport).

The all-pervading feature of the Lord is called the Supersoul. In the Bhagavad-gītā it is said, ahaṁ kṛtsnasya jagataḥ prabhavaḥ: the cosmic manifestation is a display of the energy of the Supreme Lord. The material elements (earth, water, fire, air, ether, mind, intelligence and false ego) display the inferior energy of the Lord, and the living entities are His superior energy. Since the energy of the Lord is not different from Him, in fact everything that exists is Kṛṣṇa in His impersonal feature. Sunshine, sunlight and heat are not different from the sun, and yet simultaneously they are distinct energies of the sun. Similarly, the cosmic manifestation and the living entities are energies of the Lord, and they are considered to be simultaneously one with and different from Him. The Lord therefore says, "I am everything," because everything is His energy and is therefore nondifferent from Him.
(Sri Caitanya Caritamrta----1:1:53-----purport).

The cosmic manifestation is generated by the interaction of the three modes of material nature. The transcendental world has no such material modes, although it is nevertheless full of spiritual variegatedness. In that spiritual world there are also innumerable living entities, who are eternally liberated souls engaged in transcendental loving service to Lord Kṛṣṇa. The conditioned souls, who remain within the material cosmic creation, are subjected to the threefold miseries and pangs of material nature. They exist in different species of life because they are eternally averse to transcendental loving devotion to the Supreme Lord.
(Sri Caitanya Caritamrta----1:2:36-----purport).

The primary potencies of the Absolute Truth are mentioned to be three: internal, external and marginal. By the acts of His internal potency, the Personality of Godhead in His original form exhibits the spiritual cosmic manifestations known as the Vaikuṇṭhalokas, which exist eternally, even after the destruction of the material cosmic manifestation. By His marginal potency the Lord expands Himself as living beings who are part of Him, just as the sun distributes its rays in all directions. By His external potency the Lord manifests the material creation, just as the sun with its rays creates fog. The material creation is but a perverse reflection of the eternal Vaikuṇṭha nature.
(Sri Caitanya Caritamrta----1:2:29-----purport).

Whatever is produced of the complete whole is also complete by itself. Because He is the complete whole, even though so many complete units emanate from Him, He remains the complete balance.” (Bṛhad-āraṇyaka Upaniṣad 5.1) It is most apparent that nondevotees violate the rules and regulations of devotional service to equate the whole cosmic manifestation, which is the external feature of Viṣṇu, with the Supreme Personality of Godhead, who is the controller of māyā, or with His quadruple expansions. Equating māyā with spirit, or māyā with the Lord, is a sign of atheism. The cosmic creation, which manifests life in forms from Brahmā to the ant, is the external feature of the Supreme Lord. It comprises one fourth of the Lord's energy, as confirmed in the Bhagavad-gītā (ekāṁśena sthito jagat (B.G.10:42). The cosmic manifestation of the illusory energy is material nature, and everything within material nature is made of matter. Therefore, one should not try to compare the expansions of material nature to the catur-vyūha, the quadruple expansions of the Personality of Godhead, but unfortunately the Māyāvādī school unreasonably attempts to do this.
(Sri Caitanya Caritamrta----1:5:41-----purport).

The Vedic conclusion is that the cosmic manifestation visible to the eyes of the conditioned soul is caused by the Absolute Truth, the Personality of Godhead, through the exertion of His specific energies, although in the conclusion of atheistic deliberations this manifested cosmic exhibition is attributed to material nature. The energy of the Absolute Truth is exhibited in three ways: spiritual, material and marginal. The Absolute Truth is identical with His spiritual energy. Only when contacted by the spiritual energy can the material energy work and the temporary material manifestations thus appear active. In the conditioned state the living entities of the marginal energy are a mixture of spiritual and material energies. The marginal energy is originally under the control of the spiritual energy, but, under the control of the material energy, the living entities have been wandering in forgetfulness within the material world since time immemorial.
(Sri Caitanya Caritamrta----1:5:66-----purport).

The origin of creation is the Supreme Personality of Godhead. As confirmed in the Bhagavad-gītā (9.10), the cosmic manifestation is working under the direction of the Supreme Lord, who invests the material energy with three material qualities. Agitated by these qualities, the elements supplied by the material energy produce varieties of things, just as an artist produces varieties of pictures by mixing the three colors red, yellow and blue. Yellow represents the quality of goodness, red represents passion, and blue represents ignorance. Therefore the colorful material creation is but an interaction of these three qualities, represented in eighty-one varieties of mixtures (3 x 3 equaling 9, 9 x 9 thus equaling 81). Deluded by material energy, the conditioned soul, enamored by these eighty-one varieties of manifestations, wants to lord it over material energy, just as a moth wants to enjoy a fire. This illusion is the net result of the conditioned soul's forgetfulness of his eternal relationship with the Supreme Personality of Godhead. When conditioned, the soul is impelled by the material energy to engage in sense gratification, whereas one enlightened by the spiritual energy engages himself in the service of the Supreme Lord in his eternal relationship.
(Sri Caitanya Caritamrta----1:5:66-----purport).

The Supreme Personality of Godhead then entered the universal space, and although He is invisible, He created the visible cosmic manifestation. In the material world the Supreme Personality of Godhead is not manifested by His personal presence, but the presence of the cosmic manifestation in different varieties is the proof that everything has been created under His direction. He entered the universe with all creative potencies, and thus He removed the darkness of the unlimited space.
“The form of the Supreme Personality of Godhead is described to be transcendental, very subtle, eternal, all-pervading, inconceivable and therefore nonmanifested to the material senses of a conditioned living creature. He desired to expand Himself into many living entities, and with such a desire He first created a vast expanse of water within the universal space and then impregnated that water with living entities. By that process of impregnation a massive body appeared, blazing like a thousand suns, and in that body was the first creative principle, Brahmā. The great Parāśara Ṛṣi has confirmed this in the Viṣṇu Purāṇa. He says that the cosmic manifestation visible to us is produced from Lord Viṣṇu and sustained under His protection. He is the principal maintainer and destroyer of the universal form.
“This cosmic manifestation is one of the diverse energies of the Supreme Personality of Godhead. As a spider secretes saliva and weaves a web by its own movements but at the end winds up the web within its body, so Lord Viṣṇu produces this cosmic manifestation from His transcendental body and at the end winds it up within Himself. All the great sages of the Vedic understanding have accepted that the Supreme Personality of Godhead is the original creator.
(Sri Caitanya Caritamrta----1:6:14-15-----purport).

The Supreme Brahman is the Absolute Truth, and the energies that have emanated from Him and are existing separately, such as the living entities and the cosmic manifestation, are also truths. This is an example of transformation, which is called vikāra or pariṇāma. To give another example of vikāra, milk is a truth, but the same milk may be transformed into yogurt. Thus yogurt is a transformation of milk, although the ingredients of yogurt and milk are the same.
In the Chāndogya Upaniṣad there is the following mantra: aitad-ātmyam idaṁ sarvam. This mantra indicates without a doubt that the entire world is Brahman. The Absolute Truth has inconceivable energies, as confirmed in the Śvetāśvatara Upaniṣad (parāsya śaktir vividhaiva śrūyate (Cc. Madhya 13.65, purport)), and the entire cosmic manifestation is evidence of these different energies of the Supreme Lord. The Supreme Lord is a fact, and therefore whatever is created by the Supreme Lord is also factual. Everything is true and complete (pūrṇam), but the original pūrṇam, the complete Absolute Truth, always remains the same. Pūrṇāt pūrṇam udacyate pūrṇasya pūrṇam ādāya (Īśo Invocation). The Absolute Truth is so perfect that although innumerable energies emanate from Him and manifest creations which appear to be different from Him, He nevertheless maintains His personality. He never deteriorates under any circumstances.
It is to be concluded that the entire cosmic manifestation is a transformation of the energy of the Supreme Lord, not of the Supreme Lord or Absolute Truth Himself, who always remains the same.
(Sri Caitanya Caritamrta----1:7:121-----purport).

And in the Taittirīya Upaniṣad (3.1): yato vā imāni bhūtāni jāyante, yena jātāni jīvanti, yat prayanty abhisaṁviśanti, tad vijijñāsasva tad brahma. This was the answer given by father Varuṇa when questioned by his son Vāruṇi Bhṛgu about the Absolute Truth. In this mantra, the word yataḥ, the Absolute Truth from which the cosmic manifestation has emanated, is in the ablative case; that Brahman by which this universal creation is maintained is in the instrumental case (yena); and that Brahman into which the whole cosmic manifestation merges is in the locative case (yat or yasmin). It is stated in Śrīmad-Bhāgavatam (1.5.20):
idaṁ hi viśvaṁ bhagavān ivetaro
yato jagat-sthāna-nirodha-sambhavāḥ
"The entire universal creation is contained in the gigantic form of the Supreme Personality of Godhead. Everything emanates from Him, everything rests in His energy, and after annihilation everything merges into His person."
(Sri Caitanya Caritamrta----2:6:144-----purport).