Musannaf Ibn Abi Shayba 16:842

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Muhammad ibn Ishaq, from al-Hasan ibn Zayd, from his father, that there was a lock of hair on the head of al-Hasan ibn Ali. And al-Husayn pulled him by it until he brought him near or caused him pain.