The devotees are naturally faultless. Accidental sins committed by a devotee are sincerely regretted, and by the grace of the Lord all sins unwillingly committed by a devotee are burnt in the fire of repentance.
(Srimad Bhagavatam---1:19:1---purport).

People do not consider how they are risking their lives in an attempt to have illicit sex life, kill animals to satisfy their tongue, enjoy intoxication and gamble. It is veryregrettable that the leaders of the world do not know of the effects of these sinful activities. They are instead taking things very easily and are succeeding in making the ocean of nescience wider and wider.
(Srimad Bhagavatam---4:24:75---purport).

When a person loses his Kṛṣṇa consciousness and loses interest in self-realization, he must engage in sinful activities. All one's activities in a life devoid of Kṛṣṇa consciousness simply lead to defeat and misuse of one's life. Naturally one who comes to Kṛṣṇa consciousness regrets his previous sinful activities in the human form. Only by this process can one be delivered from the clutches of nescience or ignorance in materialistic life.
(Srimad Bhagavatam---4:26:19---purport).

In this way the living entity wanders all over the universe. Only when he comes in contact with the bona fide spiritual master can he understand his real constitutional position. He then becomes disgusted with material existence. At that time, in full Kṛṣṇa consciousness, he regrets his past experiences in material existence. This regret is very beneficial because it purifies the living entity of material, conditional life. He then prays to the Lord to engage in His service, and at that time, Kṛṣṇa grants liberation from the clutches of māyā.
(Srimad Bhagavatam---4:29:29---purport).

Any person who disturbs a pure devotee engaged in broadcasting the holy name of the Lord is certainly punished like Gopāla Cāpāla. This is the instruction of Śrī Caitanya Mahāprabhu. As we shall see, one who offends a pure devotee can never satisfy Caitanya Mahāprabhu unless and until he sincerely regrets his offense and thus rectifies it.
(Sri Caitanya Caritamrta---1:17:51---purport).

If one understands what sin is, he should give it up with sincerity and regret and surrender unto the lotus feet of the Supreme Personality of Godhead through His agent, the pure devotee. In this way, one can be freed from the reactions of sin and make progress in devotional service.
(Sri Caitanya Caritamrta---2:24:253---purport).