Musnad Ahmad 5:553

Waki’ narrated to us, from Ibn Abi Layla, from al-Minhal ibn ‘Amr, from ‘Abd al-Rahman ibn Abi Layla, who said: My father used to spend the night in conversation with ‘Ali. ‘Ali used to wear summer clothes in the winter and winter clothes in the summer. It was said to me: "If only you would ask him about this?" So I asked him, and he said: "The Messenger of Allah (may Allah bless him and grant him peace) sent for me while I had an eye ailment on the day of Khaybar. I said: 'O Messenger of Allah, I have an eye ailment.' So he spat into my eyes and said: 'O Allah, remove from him the heat and the cold.' I have not felt heat or cold since then." He said: And he said: "I will certainly send a man whom Allah and His Messenger love, and who loves Allah and His Messenger; he is not one who flees." He said: So the people craned their necks for it. He said: Then he sent for ‘Ali.