al-Zuhri ابن شهاب الزهري‎, محمد بن مسلم · The Book on Sacrifices

That 'Ali used to slaughter two male sheep, one for the Prophet (ﷺ) and the other for himself. When this was mentioned to him, he said: "He ordered me to" - meaning the Prophet (ﷺ) - "So I will never leave it."

"The Messenger of Allah (ﷺ) slaughtered a horned male ram of fine pedigree, (around) his mouth was black, and his legs were black, and (around) his eyes was black.

"We were with the Messenger of Allah (ﷺ) on a journey when the (Day of) Adha came, so we shared seven for a cow and ten for a camel."

They entered upon Hafsah bint 'Abdur-Rahman to ask her about the 'Aqiqah. She informed them that 'Aishah had informed her, that the Messenger of Allah (ﷺ) ordered them that for a boy, two sheep were sufficient, and for a girl one sheep.

That his father said: "I saw the Messenger of Allah (ﷺ) say the Adhan in the ear of Al-Hasan bin 'Ali - when he was born to Fatimah - the Adhan of Salat."

That the Messenger of Allah (ﷺ) said: "The boy is mortgaged by his 'Aqiqah; slaughtering should be done for him on the seventh day, he should be given a name, and his head should be shaved."