Maliks Muwatta Book 26, Hadith Number 2.
Section : About The Aqiqa.
Yahya related to me from Malik from Jafar ibn Muhammad that his father said, “Fatima, the daughter of the Messenger of Allah, may Allah bless him and grant him peace, weighed the hair of Hasan, Husayn, Zaynab and Umm Kulthum, and gave away in sadaqa an equivalent weight of silver.”