Sayyiduna Salamah bin al-Akwa' (may Allah be pleased with him) narrates that on the day of Khaybar the Messenger of Allah (peace and blessings be upon him) said: "Today I will give this banner to a man who loves Allah and His Messenger, and whom Allah and His Messenger love." The narrator says: So he (peace and blessings be upon him) sent me to call Sayyiduna Ali (may Allah be pleased with him), while his eyes were sore. I brought him, leading him by the hand. He (peace and blessings be upon him) applied his saliva to his eye and it was cured, and he (peace and blessings be upon him) gave him the banner.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6207