Repentance comes in the mind of a good soul as soon as he commits something wrong.
(Srimad Bhagavatam---1:18:31---purport).

However sinful a man may be, if he receives knowledge from the proper spiritual master and repents his past activities in his sinful life and stops them, he immediately becomes eligible to return home, back to Godhead.
(Srimad Bhagavatam---4:26:10---purport).

The living entity is contaminated and suffering because he has a material body, but that does not mean that because the Lord is also with him, He also has a I material body. He is avikāram, changeless. He is always the same Supreme, but unfortunately the Māyāvādī philosophers, because of their impure hearts, cannot understand that the Supreme Soul, the Supersoul, is different from the individual soul. It is said here, ātapyamāna-hṛdaye 'vasitam: He is in the heart of every living entity, but He can be realized only by a soul who is repentant.
(Srimad Bhagavatam---3:31:13---purport).

The individual soul becomes repentant that he forgot his constitutional position, wanted to become one with the Supreme Soul and tried his best to lord it over material nature. He has been baffled, and therefore he is repentant.
(Srimad Bhagavatam---3:31:13---purport).

There are many cases in which a person becomes an offender to the lotus feet of a Vaiṣṇava and later becomes repentant.
(Srimad Bhagavatam---4:20:18---purport).

Bharata Mahārāja was the firstborn son of Mahārāja Ṛṣabha in a rich kṣatriya family, but due to his willful negligence of his spiritual duties and his excessive attachment to an insignificant deer, he was obliged to take birth as the son of a deer. However, due to his strong position as a devotee, he was gifted with the remembrance of his past life. Being repentant, he remained in a solitary forest and always thought of Kṛṣṇa. Then he was given the chance to take birth in a very good brāhmaṇa family.
(Srimad Bhagavatam---5:9:1-2---purport).

Jagāi and Mādhāi were two brothers born in Navadvīpa in a respectable brāhmaṇa family who later became addicted to all kinds of sinful activities. By the order of Lord Caitanya, both Nityānanda Prabhu and Haridāsa Ṭhākura used to preach the cult of Kṛṣṇa consciousness door to door. In the course of such preaching they found Jagāi and Mādhāi, two maddened drunken brothers, who, upon seeing them, began to chase them. On the next day, Mādhāi struck Nityānanda Prabhu on the head with a piece of earthen pot, thus drawing blood. When Śrī Caitanya Mahāprabhu heard of this, He immediately came to the spot, ready to punish both brothers, but when the all-merciful Lord Gaurāṅga saw Jagāi's repentant behavior, He immediately embraced him.
(Sri Caitanya Caritamrta---1:17:17---purport).

The sinful and the destitute can understand their mistakes and misfortune only by Lord Kṛṣṇa's mercy. Once they begin to repent for their sins and surrender to the Lord, they are saved; they become purified and start manifesting saintly characteristics. And if even after a person takes to the devotional process some vestige of immorality remains in his character, that also will soon be eradicated by the Lord's grace. The single-minded devotee who never offends the Supreme Lord or His devotees is to be considered a saintly soul. Even if it seems that such a saint is not yet rid of all sinful propensities, he will never be destroyed, as are the yogīs and karmīs in a similar situation. This the Supreme Lord Himself has declared.
(Renunciation Through Wisdom).