Mishkat al-Masabih 1 Faith كتاب الإيمان 87

وعنه قال : سئل رسول الله صلى الله عليه وسلم عن ذراري المشركين قال : ” الله أعلم بما كانوا عاملين ”

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.)