I heard the Prophet ﷺ say on the day of Khaybar, "I shall give the banner to a man who loves Allah and His Messenger and whom Allah and His Messenger love."He said, "We stretched our necks hoping to be the one chosen."Then he said, "Call Ali for me."Ali was brought to him suffering from sore eyes. He spat into his eyes and handed him the banner, and Allah granted him victory.
سمعت النبي ﷺ يقول: يوم خيبر: لأعطين الراية رجلا يحب الله ورسوله ويحبه الله ورسوله قال: فتطاولنا لها فقال: ادعو لي عليا فأتى به أرمد، فبصق في عينيه ودفع الراية إليه، ففتح الله عليه.
Muslim narrated it in the Book of Virtues (32:2404) through several chains from Hatim (who is Ibn Ismail), from Bukayr bin Mismar, from Amir bin Saad bin Abu Waqqas, from his father, in a long hadith which is mentioned in its place.