Muwatta Malik, Book 26, Hadith 1072 (In-Book) ⓘ

Yahya related to me from Malik from Rabia ibn Abi Abd ar-Rahman that Muhammad ibn Ali ibn al-Husayn said, "Fatima, the daughter of the Messenger of Allah, may Allah bless him and grant him peace, weighed the hair of Hasan and Husayn, and gave away in sadaqa the equivalent weight in silver."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ رَبِيعَةَ بْنِ أَبِي عَبْدِ الرَّحْمَنِ، عَنْ مُحَمَّدِ بْنِ عَلِيِّ بْنِ الْحُسَيْنِ، أَنَّهُ قَالَ وَزَنَتْ فَاطِمَةُ بِنْتُ رَسُولِ اللَّهِ صلى الله عليه وسلم شَعَرَ حَسَنٍ وَحُسَيْنٍ فَتَصَدَّقَتْ بِزِنَتِهِ فِضَّةً ‏.‏