It is narrated from Sayyiduna Ali (may Allah be pleased with him) that I heard a man supplicating for forgiveness for his polytheist parents, so I said, "Can a person supplicate for forgiveness for his polytheist parents?" He replied, "Did not Prophet Ibrahim (peace be upon him) supplicate for forgiveness for his father?" I mentioned this to the Prophet (peace and blessings be upon him), so this verse was revealed: «﴿مَاكَانَلِلنَّبِيِّوَالَّذِينَآمَنُواأَنْيَسْتَغْفِرُوالِلْمُشْرِكِينَ﴾ [التوبة : 113]» "It is not appropriate for the Prophet and the believers to seek forgiveness for the polytheists."
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 771