Musannaf Ibn Abi Shayba 18:805

Abu Bakr narrated to us, he said: Abd al-Rahim ibn Sulayman narrated to us, from Hajjaj, from Jundub al-Qadi, from Aslam, the freed slave of Umar, from Umar: That he decreed regarding the tooth of a young boy, if it falls out before he reaches the age of puberty (i.e., before his permanent teeth grow), that a camel is to be paid as compensation.