The Prophet ﷺ said, "I will give the banner to a man who loves Allah and His Messenger," or he said, "whom Allah and His Messenger love." He then called for Ali, who was suffering from sore eyes, and Allah granted victory at his hands.
أن النبي ﷺ قال: لأعطين الراية رجلا يحب الله ورسوله- أو قال-: يحبه الله ورسوله. فدعا عليا وهو أرمد، ففتح الله على يديه.
Nasai narrated it in Kubra (8094, 8353), and Tabarani in Kabir (18/237), both through the route of Mutamir bin Sulayman, from his father, from Mansur, from Rabi bin Harash, from Imran bin Husayn, who said, then he related it. Its isnad is sahih.It has been narrated from Abdul-Rahman bin Abu Layla, who said, "My father used to stay up at night talking with Ali. Ali would wear summer clothes in winter and winter clothes in summer, so it was suggested to him, 'Why not ask him about it?' So he asked him, and Ali said, 'The Messenger of Allah ﷺ sent for me while I had inflamed eyes on the day of Khaybar. I said, "Messenger of Allah, my eyes are inflamed." He spat in my eye and said, "O Allah, take away from him the heat and the cold." From that day on I have never felt heat or cold. He then said, "I will give this banner to a man who loves Allah and His Messenger, and whom Allah and His Messenger love, one who does not flee." The companions of the Prophet ﷺ all hoped to be chosen for it, but he gave it to me.'"Ahmad narrated it (778) from Waki, from Ibn Abu Layla (that is, Muhammad bin Abdul-Rahman bin Abu Layla), from Minhal bin Amr, from Abdul-Rahman bin Abu Layla, who related it.Ibn Majah narrated it (117) from Uthman bin Abu Shayba, who said, Waki told us, Ibn Abu Layla told us, Hakam (that is, Ibn Utayba) told us, from Abdul-Rahman bin Abu Layla, who related it.Bazzar narrated it (496) from Yusuf bin Musa, who said, Ubaydullah bin Musa told us, Ibn Abu Layla told us, from Hakam and Minhal, from Abdul-Rahman bin Abu Layla, from his father, who said, then he related it in a longer form.The pivot of all these routes is Muhammad bin Abdul-Rahman bin Abu Layla, who is daif, extremely poor in memory, and this is why he was inconsistent in naming his teachers. Shuba said, "I have never seen anyone with worse memory than Ibn Abu Layla," and Ahmad, Abu Hatim, and others said the same. Busiri faulted the hadith on this basis in Misbah Zujaja.Abu Layla's given name was Yasar. The hadith has also been narrated through other routes from Ali, but all of them are daif.