The Book of Funerals
21/60. Chapter:
The Children Of The Idolaters
Sunan an-Nasai
أَخْبَرَنِي مُجَاهِدُ بْنُ مُوسَى، عَنْ هُشَيْمٍ، عَنْ أَبِي بِشْرٍ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ سُئِلَ النَّبِيُّ صلى الله عليه وسلم عَنْ ذَرَارِيِّ الْمُشْرِكِينَ فَقَالَ " اللَّهُ أَعْلَمُ بِمَا كَانُوا عَامِلِينَ " .
It was narrated that Ibn 'Abbas said: "The Messenger of Allah was asked about he children of the idolators and he said: 'Allah knows best what they would have done."'
Reference : Sunan an-Nasa'i 1952In-book reference : Book 21, Hadith 135English translation : Vol. 3, Book 21, Hadith 1954