Musannaf Ibn Abi Shayba 16:314

Abu Bakr narrated to us, he said: Waki’ narrated to us, from ‘Abdullah bin Sa’id, from Muhammad bin ‘Abdullah bin ‘Amr bin ‘Uthman, from his mother, Fatimah bint Husayn, from Ibn ‘Abbas, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Do not persist in looking at those afflicted with leprosy."