وَمَا كَانَ ٱسْتِغْفَارُ إِبْرَٰهِيمَ لِأَبِيهِ إِلَّا عَن مَّوْعِدَةٍ وَعَدَهَآ إِيَّاهُ فَلَمَّا تَبَيَّنَ لَهُۥٓ أَنَّهُۥ عَدُوٌّ لِّلَّهِ تَبَرَّأَ مِنْهُ ۚ إِنَّ إِبْرَٰهِيمَ لَأَوَّٰهٌ حَلِيمٌ
“As for Abraham's prayer for his father's forgiveness, it was only in fulfillment of a promise he had made to him. But when it became clear to Abraham that his father was an enemy of Allah, he broke ties with him. Abraham was truly tender-hearted, forbearing.”
Part of the same Abraham's-prayer-for-his-father passage as 9:113 (already linked to this event), explaining the limits of seeking forgiveness for a mushrik relative.