Musannaf Ibn Abi Shayba 27:458

Ya'la ibn 'Ubayd narrated to us, from Abu Munin—and he is Yazid ibn Kaysan—from Abu Hazim, from Abu Hurayrah, who said: The Messenger of Allah (ﷺ) said: "I shall certainly hand over the banner to a man who loves Allah and His Messenger." He said: The people stretched themselves [to be seen]. Then he said: "Where is Ali?" They said: "He is complaining of his eyes." So he called him, and he spat into his palms, and wiped Ali's eyes with them. Then he handed the banner to him, and Allah granted him victory on that day.