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كتاب المغازى
64  
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
(30)
Chapter: The return of the Prophet (saws) from Ahzab and his going out to Bani Quraiza
(30)
بَابُ مَرْجَعِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مِنَ الأَحْزَابِ وَمَخْرَجِهِ إِلَى بَنِي قُرَيْظَةَ وَمُحَاصَرَتِهِ إِيَّاهُمْ
Sahih al-Bukhari 4123

Narrated Al-Bara:

The Prophet (ﷺ) said to Hassan, "Abuse them (with your poems), and Gabriel is with you (i.e, supports you)." (Through another group of sub narrators) Al-Bara bin Azib said, "On the day of Quraiza's (besiege), Allah's Messenger (ﷺ) said to Hassan bin Thabit, 'Abuse them (with your poems), and Gabriel is with you (i.e. supports you).' "

حَدَّثَنَا الْحَجَّاجُ بْنُ مِنْهَالٍ، أَخْبَرَنَا شُعْبَةُ، قَالَ أَخْبَرَنِي عَدِيٌّ، أَنَّهُ سَمِعَ الْبَرَاءَ ـ رضى الله عنه ـ قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم لِحَسَّانَ ‏ "‏ اهْجُهُمْ ـ أَوْ هَاجِهِمْ ـ وَجِبْرِيلُ مَعَكَ ‏"‏‏.‏
Reference : Sahih al-Bukhari 4123
In-book reference : Book 64, Hadith 167
USC-MSA web (English) reference : Vol. 5, Book 59, Hadith 449
  (deprecated numbering scheme)