Musannaf Ibn Abi Shayba 9:1377

Waki’ narrated to us, from Sufyan, from al-A’mash, from ‘Amr ibn Murrah, from Abu al-Bakhtari, from Abu Salih, that al-Hasan and al-Husayn used to enter upon their sister, Umm Kulthum, while she was combing [her hair].