Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The angel on the left side (who writes bad deeds) holds back his pen from writing the mistake of a Muslim servant who makes a mistake for six hours. If (within that time) the Muslim regrets and seeks forgiveness from Allah, the angel puts down his pen (i.e., the sin is not written at all). But if he does not get the opportunity to feel remorse within that time, then the angel writes one bad deed."