(30) بَابُ مَرْجَعِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مِنَ الأَحْزَابِ وَمَخْرَجِهِ إِلَى بَنِي قُرَيْظَةَ وَمُحَاصَرَتِهِ إِيَّاهُمْ
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).' "
Reference: Sahih al-Bukhari 4123
In-book reference: Book 64, Hadith 167
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 5, Book 59, Hadith 449