The Holy Quran

مَا كَانَ لِلنَّبِيِّ وَالَّذِينَ آمَنُواْ أَن يَسْتَغْفِرُواْ لِلْمُشْرِكِينَ وَلَوْ كَانُواْ أُوْلِي قُرْبَى مِن بَعْدِ مَا تَبَيَّنَ لَهُمْ أَنَّهُمْ أَصْحَابُ الْجَحِيمِ

It is not for the Prophet, and those who believe, to pray for the forgiveness of idolaters even though they may be near of kin (to them) after it hath become clear that they are people of hell fire.