Majma al-Zawaid 10171 — The date of the Battle of the Trench

Muhammad bin Ishaq narrates: The Battle of the Trench took place in the month of Shawwal, in the year 5 AH, and during it Sayyiduna Sa'd bin Mu'adh (may Allah be pleased with him) passed away (that is, during it he was wounded, and that wound became the cause of his death).
Al-Tabarani recorded it, and its narrators are thiqat (trustworthy).