Sahih al-Bukhari, Hadith 3009 ⓘ

Narrated Sahl: On the day (of the battle) of Khaibar the Prophet said, "Tomorrow I will give the flag to somebody who will be given victory (by Allah) and who loves Allah and His Apostle and is loved by Allah and His Apostle." So, the people wondered all that night as to who would receive the flag and in the morning everyone hoped that he would be that person. Allah's Messenger asked, "Where is `Ali?" He was told that `Ali was suffering from eye-trouble, so he applied saliva to his eyes and invoked Allah to cure him. He at once got cured as if he had no ailment. The Prophet gave him the flag. `Ali said, "Should I fight them till they become like us (i.e. Muslim)?" The Prophet said, "Go to them patiently and calmly till you enter the land. Then, invite them to Islam, and inform them what is enjoined upon them, for, by Allah, if Allah gives guidance to somebody through you, it is better for you than possessing red camels."

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا يَعْقُوبُ بْنُ عَبْدِ الرَّحْمَنِ بْنِ مُحَمَّدِ بْنِ عَبْدِ اللَّهِ بْنِ عَبْدٍ الْقَارِيُّ، عَنْ أَبِي حَازِمٍ، قَالَ أَخْبَرَنِي سَهْلٌ ـ رضى الله عنه يَعْنِي ابْنَ سَعْدٍ ـ قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم يَوْمَ خَيْبَرَ ‏"‏ لأُعْطِيَنَّ الرَّايَةَ غَدًا رَجُلاً يُفْتَحُ عَلَى يَدَيْهِ، يُحِبُّ اللَّهَ وَرَسُولَهُ، وَيُحِبُّهُ اللَّهُ وَرَسُولُهُ ‏"‏‏.‏ فَبَاتَ النَّاسُ لَيْلَتَهُمْ أَيُّهُمْ يُعْطَى فَغَدَوْا كُلُّهُمْ يَرْجُوهُ فَقَالَ ‏"‏ أَيْنَ عَلِيٌّ ‏"‏‏.‏ فَقِيلَ يَشْتَكِي عَيْنَيْهِ، فَبَصَقَ فِي عَيْنَيْهِ وَدَعَا لَهُ، فَبَرَأَ كَأَنْ لَمْ يَكُنْ بِهِ وَجَعٌ، فَأَعْطَاهُ فَقَالَ أُقَاتِلُهُمْ حَتَّى يَكُونُوا مِثْلَنَا‏.‏ فَقَالَ ‏"‏ انْفُذْ عَلَى رِسْلِكَ حَتَّى تَنْزِلَ بِسَاحَتِهِمْ، ثُمَّ ادْعُهُمْ إِلَى الإِسْلاَمِ، وَأَخْبِرْهُمْ بِمَا يَجِبُ عَلَيْهِمْ، فَوَاللَّهِ لأَنْ يَهْدِيَ اللَّهُ بِكَ رَجُلاً خَيْرٌ لَكَ مِنْ أَنْ يَكُونَ لَكَ حُمْرُ النَّعَمِ ‏"‏‏.‏