The only reason Abraham asked forgiveness for his father was that he had promised him to do so. But as soon as he realized that he was an enemy of God, he disowned him. Abraham was extremely kind, clement.
وَما كانَ استِغفارُ إِبرٰهيمَ لِأَبيهِ إِلّا عَن مَوعِدَةٍ وَعَدَها إِيّاهُ فَلَمّا تَبَيَّنَ لَهُ أَنَّهُ عَدُوٌّ لِلَّهِ تَبَرَّأَ مِنهُ إِنَّ إِبرٰهيمَ لَأَوّٰهٌ حَليمٌ
wa maa kaanas tighfaaru ibraaheema li abeehi illaa ‘an maw’idatinw wa ‘adahaaa iyyaahu falammaa tabaiyana lahooo annahoo ‘aduwwul lillaahi tabarra a minh; inna Ibraaheema la awwaahun haleem