Narrated 'Ali:
"I heard a man seeking forgiveness for his parents who were idolaters, so I said to him: 'You seek forgiveness for your parents while they are idolaters?' He said: 'Did Ibrahim not seek forgiveness for his father, and he was an idolater?' So I mentioned that to the Prophet (ﷺ) and (the following) was revealed: It is not for the Prophet nor those who believe, that they should seek forgiveness for the idolaters (9:113)." (DE)
English reference (DE): Vol. 5, Book 44, Hadith 3101 (DE)
Arabic reference (DE): Book 47, Hadith 3384 (DE)