Musannaf Ibn Abi Shayba 16:16

Abu Bakr narrated to us, he said: Affan narrated to us, he said: Hammad bin Salamah narrated to us, from Abdullah bin Uthman, from Yusuf bin Mahak, from Hafsah bint Abd al-Rahman, from Aisha, that she said: The Messenger of Allah, peace and blessings of Allah be upon him, commanded us to sacrifice two sheep for a boy and one sheep for a girl.