Musannaf Ibn Abi Shayba 16:5

Abu Bakr narrated to us, he said: Muhammad ibn Abdullah al-Asadi narrated to us, from Sharik, from Ibn Aqil, from Ali ibn al-Husayn, from Abu Rafi, who said: Fatima said: "O Messenger of Allah, shall I sacrifice blood (an animal) for my son?" He said: "No, but shave his head and give in charity the weight of his hair to the poor in ounces of silver."