Musannaf Ibn Abi Shayba 13:2290

Abu Bakr narrated to us, he said: Sufyan narrated to us, from Abu al-Nadr, from Abu Anas, he said: I heard Uthman saying: Do not burden the young child with earning, for he will steal. And do not burden the slave girl who is not skilled with a craft, for she will earn through her private parts. Pardon, for Allah has pardoned you. And upon you are the earnings that are lawful for you.