Sahih Bukhari Volume 5, Book 64, Hadith 4211

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، حَدَّثَنَا حَاتِمٌ، عَنْ يَزِيدَ بْنِ أَبِي عُبَيْدٍ، عَنْ سَلَمَةَ، رضى الله عنه قَالَ كَانَ عَلِيٌّ ـ رضى الله عنه ـ تَخَلَّفَ عَنِ النَّبِيِّ صلى الله عليه وسلم فِي خَيْبَرَ، وَكَانَ رَمِدًا فَقَالَ أَنَا أَتَخَلَّفُ عَنِ النَّبِيِّ صلى الله عليه وسلم فَلَحِقَ، فَلَمَّا بِتْنَا اللَّيْلَةَ الَّتِي فُتِحَتْ قَالَ ‏"‏ لأُعْطِيَنَّ الرَّايَةَ غَدًا ـ أَوْ لَيَأْخُذَنَّ الرَّايَةَ غَدًا ـ رَجُلٌ يُحِبُّهُ اللَّهُ وَرَسُولُهُ، يُفْتَحُ عَلَيْهِ ‏"‏‏.‏ فَنَحْنُ نَرْجُوهَا فَقِيلَ هَذَا عَلِيٌّ، فَأَعْطَاهُ فَفُتِحَ عَلَيْهِ‏

Narrated By Salama : Ali remained behind the Prophet during the Ghazwa of Khaibar as he was suffering from eye trouble. He then said, "(How can) I remain behind the Prophet ," and followed him. So when he slept on the night of the conquest of Khaibar, the Prophet said, "I will give the flag tomorrow, or tomorrow the flag will be taken by a man who is loved by Allah and His Apostle , and (Khaibar) will be conquered through him, (with Allah's help)" While every one of us was hopeful to have the flag, it was said, "Here is 'Ali" and the Prophet gave him the flag and Khaibar was conquered through him (with Allah's Help).