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."' Translation Not Available

Book Ref: Sunan An Nisai Book 21 Hadith 1952
Web Ref:  Sunan An Nisai Vol 3 Book 21 Hadith 1954