Sahih al-Bukhari 3702
Companions of the Prophet
The merits of 'Ali bin Abi Talib رضي الله عنه
Narrated Salama: `Ali happened to stay behind the Prophet (ﷺ) and (did not join him) during the battle of Khaibar for he was having eye trouble. Then he said, "How could I remain behind Allah's Messenger (ﷺ) ?" So `Ali set out following the Prophet (ﷺ) , When it was the eve of the day in the morning of which Allah helped (the Muslims) to conquer it, Allah's Messenger (ﷺ) said, "I will give the flag (to a man), or tomorrow a man whom Allah and His Messenger love will take the flag," or said, "A man who loves Allah and His Messenger; and Allah will grant victory under his leadership." Suddenly came `Ali whom we did not expect. The people said, "This is `Ali." Allah's Messenger (ﷺ) gave him the flag and Allah granted victory under his leadership.