Musannaf Ibn Abi Shayba 33:492

Mu'awiyah ibn Hisham narrated to us, he said: Sufyan narrated to us, from Sulayman al-Taymi, from Abu Uthman al-Nahdi, he said: We sent a woman to Abdullah ibn Amr to ask him: "What is the sin that Allah does not forgive?" He said: "There is no sin or deed between the heaven [and the earth] that a servant repents to Allah the Exalted for before death, except that He accepts his repentance."