Musnad Ahmad 25:237

Waki’ narrated to us, Abdullah bin Sa’id bin Abi Hind narrated to me, from Muhammad bin Abdullah bin ‘Amr bin ‘Uthman, from his mother, Fatimah bint Husayn, from Ibn Abbas, and Safwan; Abdullah bin Sa’id bin Abi Hind informed us, from Muhammad bin Abdullah bin ‘Amr bin ‘Uthman, from his mother, Fatimah bint Husayn, that she heard Ibn Abbas saying: The Messenger of Allah (ﷺ) said: "Do not persist in looking at those afflicted with leprosy."