Musannaf Ibn Abi Shayba 27:442

Ali ibn Hashim narrated to us, from Ibn Abi Layla, from al-Hakam, al-Minhal, and Isa, from Abd al-Rahman ibn Abi Layla, who said: Ali used to go out in the winter in an izar (waist-wrapper) and a rida (upper garment)—two light garments—and in the summer in a padded qaba (tunic) and a heavy garment. The people said to Abd al-Rahman, "If only you would speak to your father, for he stays up late with him." So I asked my father and said, "The people have seen something from the Commander of the Faithful that they find strange." He said, "And what is that?" I said, "He goes out in the intense heat in a padded qaba and a heavy garment, and he does not mind that. And he goes out in the intense cold in two light garments and two sheets, and he does not mind that, nor does he protect himself from the cold. Have you heard anything about that? They have ordered me to ask you to ask him when you spend the evening with him." So he spent the evening with him and said, "O Commander of the Faithful, the people have noticed something about you." He said, "And what is it?" He said, "You go out in the intense heat in a padded qaba and a heavy garment, and you go out in the intense cold in two light garments and two sheets, and you do not mind that, nor do you protect yourself from the cold." He said, "Were you not with us at Khaybar, O Abu Layla?" He said, "I said, 'Yes, by Allah, I was with you.'" He said, "The Messenger of Allah (peace and blessings of Allah be upon him) sent Abu Bakr, and he marched with the people, but he was defeated until he returned to him. Then he sent Umar, and he was defeated with the people until he reached him. Then the Messenger of Allah (peace and blessings of Allah be upon him) said, 'I will certainly give the banner to a man who loves Allah and His Messenger, and whom Allah and His Messenger love; Allah will grant victory at his hands; he is not one who flees.' So he sent for me and called me. I came to him while I was suffering from eye inflammation, unable to see anything. He spat into my eyes and said, 'O Allah, protect him from the heat and the cold.' He said, 'No heat or cold has harmed me since then.'"