The Lord says in Bhagavad-gītā (2.12), "Never was there a time when I did not exist, nor you, nor all these kings; nor in the future shall any of us cease to be." Thus the Lord's person is the Absolute Truth in the past, present and future.
In this regard, Madhvācārya quotes two verses from the Matsya Purāṇa:
nānā-varṇo haris tv eko
bahu-śīrṣa-bhujo rūpāt
āsīl laye tad-anyat tu
sūkṣma-rūpaṁ śriyaṁ vinā
asuptaḥ supta iva ca
mīlitākṣo 'bhavad dhariḥ
anyatrānādarād viṣṇau
śrīś ca līneva kathyate
sūkṣmatvena harau sthānāl
līnam anyad apīṣyate
After the annihilation of everything, the Supreme Lord, because of His sac-cid-ānanda-vigraha (Bs. 5.1), remains in His original form, but since the other living entities have material bodies, the matter merges into matter, and the subtle form of the spirit soul remains within the body of the Lord. The Lord does not sleep, but the ordinary living entities remain asleep until the next creation. An unintelligent person thinks that the opulence of the Supreme Lord is nonexistent after the annihilation, but that is not a fact. The opulence of the Supreme Personality of Godhead remains as it is in the spiritual world; only in the material world is everything dissolved. Brahma-līna, merging into the Supreme Brahman, is not actual līna, or annihilation, for the subtle form remaining in the Brahman effulgence will return to the material world after the material creation and again assume a material form.
(Srimad Bhagavatam----6:4:47----purport).

In the Matsya Purāṇa it is said:
ananta-śaktir bhagavān
matsya-rūpī janārdanaḥ
krīḍārthaṁ yācayām āsa
svayaṁ satyavrataṁ nṛpam
"The Supreme Personality of Godhead possesses unlimited potency. Nonetheless, in His pastime in the form of a fish He begged protection from King Satyavrata."
(Srimad Bhagavatam----8:24:14----purport).