Musannaf Ibn Abi Shayba 36:361

Ya'la ibn 'Ubayd narrated to us, he said: Abu Munin narrated to us, from Abu Hazim, from Abu Hurayrah, who said: The Prophet of Allah (may Allah bless him and grant him peace) said: "I will certainly hand over the banner today to a man whom Allah and His Messenger love." The people stretched themselves [to be seen], then he said: "Where is 'Ali?" They said: "He is complaining of his eye." So he called him, and he spat into his palms and wiped the eyes of 'Ali with them. Then he handed the banner to him, and Allah granted him victory on that day.