أَخْبَرَنَا إِسْحَاقُ، قَالَ أَنْبَأَنَا سُفْيَانُ، عَنِ الزُّهْرِيِّ، عَنْ عَطَاءِ بْنِ يَزِيدَ اللَّيْثِيِّ، عَنْ أَبِي هُرَيْرَةَ، قَالَ سُئِلَ رَسُولُ اللَّهِ صلى الله عليه وسلم عَنْ أَوْلاَدِ الْمُشْرِكِينَ فَقَالَ ‏"‏ اللَّهُ أَعْلَمُ بِمَا كَانُوا عَامِلِينَ ‏"‏ ‏.‏

It was narrated that Abu Hurairah said: "The Messenger of Allah was asked about the children of the idolators and he said: 'Allah knows best what they would have done."' Translation Not Available

Book Ref: Sunan An Nisai Book 21 Hadith 1949
Web Ref:  Sunan An Nisai Vol 3 Book 21 Hadith 1951