Musannaf Ibn Abi Shayba 17:1105

Waki' narrated to us, from Abdullah bin Sa'id, from Muhammad bin Abdullah bin Amr bin Uthman, from his mother, Fatima bint Husayn, from Ibn Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not persist in looking at those afflicted with leprosy."