Musnad Ahmad 1085
Musnad 'Ali Ibn Abi Talib
It was narrated from Abul-Khaleel that ‘Ali (رضي الله عنه) said: I heard a man asking for forgiveness for his parents and they were mushrikeen. I said: Are you asking for forgiveness for your parents when they are mushrikeen? He said: Didn`t Ibraheem (عليه السلام) ask for forgiveness for his father when he was a mushrik? I mentioned that to the Prophet (ﷺ) and these verses were revealed: “It is not (proper) for the Prophet (ﷺ) and those who believe to ask Allah`s forgiveness for the Mushrikeen” [At-Tawbah 9:113-114]. ‘Abdur-Rahman said: And Allah revealed [the words]. “And Ibraheem`s (Abraham) invoking (of Allah) for his father`s forgiveness was only because of a promise he [Ibraheem (Abraham)] had made to him (his father)`.