Sahih Muslim Book 37, Hadith Number 6658.

Chapter : The words of Allah “The good deeds take away the evil deeds”.

‘Abdullah reported that a person came to Allah’s Apostle (may peace be upon him) and said: Allah’s Messenger, I sported with a woman in the outskirts of Medina, and I have committed an offence short of fornication. Here I am (before you), kindly deliver verdict about me which you deem fit. Unar said: Allah concealed your fault. You had better conceal it yourself also. Allah’s Apostle (may peace be upon him), however, gave no reply to him. The man stood up and went away and Allah’s Apostle (may peace be upon him) sent a person after him to call him and be recited this verse: “And observe prayer at the ends of the day and in the first hours of the night. Surely, good deeds take away evil deeds. That is a reminder for the mindful” (xi. l15). A person amongst the people said: Allah’s Apostle, does it concern this marn only? Thereupon he (the Holy Prophet) said: No, but the people at large.