The father of Bukayr bin al-Akhnas said: We differed over the reading of this verse: 'And He knows what you do' or 'what they do' [Surah al-Shura: 25]. So I went to Sayyiduna Ibn Mas'ud (may Allah be pleased with him) to ask him about it. While I was with him, someone came and said: O Abu Abd al-Rahman! A man committed indecency with his wife (before marriage), then both of them repented and reformed themselves. So Sayyiduna Abdullah (may Allah be pleased with him) recited this verse: "And it is He who accepts repentance from His servants, pardons evil deeds, and knows what you do" [Surah al-Shura: 25].
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9634