At-Tawbah 9:113

Ma kana linnabiyyi wallatheenaamanoo an yastaghfiroo lilmushrikeena walaw kanooolee qurba min baAAdi ma tabayyana lahum annahum as-habualjaheem

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.

It is not (permissible) for the Prophet and the believers to seek forgiveness for the Mushriks, even if they are kinsmen, after it became clear to them that they are the people of hell.