Musnad Ahmad 5:216

Waki’ narrated to us, from Ibn Abi Layla, from al-Minhal, from ‘Abd al-Rahman ibn Abi Layla, who said: My father used to spend the evening with ‘Ali, and ‘Ali used to wear summer clothes in the winter and winter clothes in the summer. It was said to him: "Would you ask him?" So he asked him, and he said: "The Messenger of Allah (may Allah bless him and grant him peace) sent for me while I was suffering from eye inflammation on the day of Khaybar. I said: 'O Messenger of Allah, I am suffering from eye inflammation.' 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 that day." He also said: "I will certainly give the banner to a man who loves Allah and His Messenger, and whom Allah and His Messenger love; he is not one who flees." The companions of the Prophet (may Allah bless him and grant him peace) stood up hoping for it, but he gave it to me.