Sahih Bukhari

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 Apostle love will take the flag,"" or said, ""A man who loves Allah and His Apostle; 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