Musnad Ahmad 1268:1

Hushaym narrated to us, he said: Mansur informed us, from ‘Ata’, from Umm Kurz al-Ka‘biyyah al-Khath‘amiyyah, from the Prophet, peace and blessings of Allah be upon him, regarding the ‘Aqiqah (sacrifice for a newborn). He said: "For the boy, two equivalent sheep, and for the girl, one sheep."