Musnad Ahmad 5:209

Yahya ibn Adam narrated to us, Sufyan narrated to us, from Abu Ishaq, from Abu al-Khalil, from Ali, who said: I heard a man seeking forgiveness for his parents while they were polytheists. I said: "Does a man seek forgiveness for his parents while they are polytheists?" He replied: "Did Ibrahim not seek forgiveness for his father?" I mentioned that to the Prophet, peace and blessings of Allah be upon him, and then it was revealed: "It is not for the Prophet and those who have believed to ask forgiveness for the polytheists" [At-Tawbah: 113] up to His saying: "he disassociated himself from him" [At-Tawbah: 114]. He said: "When he died." I do not know if Sufyan said it, or if Isra'il said it, or if it is in the hadith: "When he died?"