Ubaydullah bin 'Abdullah bin 'Utba عبيد الله بن عبد الله بن عتبة بن مسعود · The Book on Sacrifices

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."