Musannaf Ibn Abi Shayba 16:13

Abu Bakr narrated to us, he said: Ibn Idris narrated to us, from Aslam, from Ata, that Umm al-Siba’ asked the Messenger of Allah, may Allah bless him and grant him peace: "Should I perform the 'aqiqah for my children?" He said: "Yes. For the boy, two sheep, and for the girl, one sheep."