Musnad Ahmad 1268:6

Muhammad ibn Bakr narrated to us, he said: Ibn Jurayj informed us, he said: Ubayd Allah ibn Abi Yazid informed me that Siba’ ibn Thabit, the cousin of Muhammad ibn Thabit ibn Siba’, informed him that Umm Kurz informed her that she asked the Prophet, peace and blessings of Allah be upon him, about the *aqiqah* (sacrifice for a newborn), and he mentioned it.