The son of Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) reports from his father that the Prophet (peace and blessings be upon him) said: "Remorse is repentance, and the one who repents from sin is like one who has no sin."
Al-Tabarani recorded it; its chain contains narrators whom I do not know.
Allamah al-Haythami says: I say: Some hadiths on this subject have already passed in Kitab al-Iman, in the chapter: Islam wipes out what came before it (that is, sins).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب التوبة / 17527