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.
حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا حَاتِمٌ، عَنْ يَزِيدَ بْنِ أَبِي عُبَيْدٍ، عَنْ سَلَمَةَ، قَالَ كَانَ عَلِيٌّ قَدْ تَخَلَّفَ عَنِ النَّبِيِّ صلى الله عليه وسلم فِي خَيْبَرَ وَكَانَ بِهِ رَمَدٌ فَقَالَ أَنَا أَتَخَلَّفُ عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم فَخَرَجَ عَلِيٌّ فَلَحِقَ بِالنَّبِيِّ صلى الله عليه وسلم، فَلَمَّا كَانَ مَسَاءُ اللَّيْلَةِ الَّتِي فَتَحَهَا اللَّهُ فِي صَبَاحِهَا، قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لأُعْطِيَنَّ الرَّايَةَ ـ أَوْ لَيَأْخُذَنَّ الرَّايَةَ ـ غَدًا رَجُلاً يُحِبُّهُ اللَّهُ وَرَسُولُهُ ـ أَوْ قَالَ يُحِبُّ اللَّهَ وَرَسُولَهُ ـ يَفْتَحُ اللَّهُ عَلَيْهِ ". فَإِذَا نَحْنُ بِعَلِيٍّ وَمَا نَرْجُوهُ، فَقَالُوا هَذَا عَلِيٌّ. فَأَعْطَاهُ رَسُولُ اللَّهِ صلى الله عليه وسلم فَفَتَحَ اللَّهُ عَلَيْهِ.
Bukhari
Companions of the Prophet • Hadith 52