Hadith 1:87
Muttafaqun 'alayh (Zubair `Aliza'i)
He also reported that when God’s messenger was questioned about the offspring of polytheists he said, “God knows best about what they were doing.” (Bukhari and Muslim.)
وعنه قال : سئل رسول الله صلى الله عليه وسلم عن ذراري المشركين قال : " الله أعلم بما كانوا عاملين "
Original Reference: Mishkat al-Masabih 93