Sunan Ibn Majah, Chapter: The Book of the Sunnah

the Mother of the Believers said: "The Messenger of Allah (saw) was called to the funeral of a child from among the Ansar. I said: 'O Messenger of Allah, glad tidings for him! He is one of the little birds of Paradise, who never did evil or reached the age of doing evil (i.e., the age of accountability).' He said: 'It may not be so, O 'Aishah! For Allah has created people for Paradise, He created them for it when they were still in their fathers' loins. And He has created people for Hell, He created them for it when they were still in their fathers' loins.'" (Sahih)