SB 10.16.35

In this regard Śrīla Prabhupāda comments in his Kṛṣṇa, the Supreme Personality of Godhead, Chapter Sixteen: “The Nāgapatnīs confirm that one cannot come in contact with Kṛṣṇa without having executed pious activities in devotional service in his previous lives. As Lord Caitanya advised in His Śikṣāṣṭaka, one has to execute devotional service by humbly chanting the Hare Kṛṣṇa mantra, thinking oneself lower than the straw in the street and not expecting honor for himself but offering all kinds of honor to others. The Nāgapatnīs were astonished that, although Kāliya had the body of a serpent as the result of grievous sinful activities, at the same time he was in contact with the Lord to the extent that the Lord’s lotus feet were touching his hoods. Certainly this was not the ordinary result of pious activities. These two contradictory facts astonished them.”