It is not for the Prophet and those who have believed to ask forgiveness for the polytheists, even if they were relatives, after it has become clear to them that they are companions of Hellfire.  

مَا كَانَ لِلنَّبِيِّ وَالَّذِينَ آمَنُوا أَنْ يَسْتَغْفِرُوا لِلْمُشْرِكِينَ وَلَوْ كَانُوا أُولِي قُرْبَىٰ مِنْ بَعْدِ مَا تَبَيَّنَ لَهُمْ أَنَّهُمْ أَصْحَابُ الْجَحِيمِ  

And the request of forgiveness of Abraham for his father was only because of a promise he had made to him. But when it became apparent to Abraham that his father was an enemy to Allah, he disassociated himself from him. Indeed was Abraham compassionate and patient.  

وَمَا كَانَ اسْتِغْفَارُ إِبْرَاهِيمَ لِأَبِيهِ إِلَّا عَنْ مَوْعِدَةٍ وَعَدَهَا إِيَّاهُ فَلَمَّا تَبَيَّنَ لَهُ أَنَّهُ عَدُوٌّ لِلَّهِ تَبَرَّأَ مِنْهُ ۚ إِنَّ إِبْرَاهِيمَ لَأَوَّاهٌ حَلِيمٌ  

And Allah would not let a people stray after He has guided them until He makes clear to them what they should avoid. Indeed, Allah is Knowing of all things.  

وَمَا كَانَ اللَّهُ لِيُضِلَّ قَوْمًا بَعْدَ إِذْ هَدَاهُمْ حَتَّىٰ يُبَيِّنَ لَهُمْ مَا يَتَّقُونَ ۚ إِنَّ اللَّهَ بِكُلِّ شَيْءٍ عَلِيمٌ  

Indeed, to Allah belongs the dominion of the heavens and the earth; He gives life and causes death. And you have not besides Allah any protector or any helper.  

إِنَّ اللَّهَ لَهُ مُلْكُ السَّمَاوَاتِ وَالْأَرْضِ ۖ يُحْيِي وَيُمِيتُ ۚ وَمَا لَكُمْ مِنْ دُونِ اللَّهِ مِنْ وَلِيٍّ وَلَا نَصِيرٍ