Sa'd was wounded on the day of the Battle of the Ditch. A man from the Quraish called Ibn al-Ariqah shot at him an arrow which pierced the artery in the middle of his forearm. The Messenger of Allah ﷺ pitched a tent for him in the mosque and would inquire after him being in close proximity. When he returned from the Ditch and laid down his arms and took a bath, the angel Gabriel appeared to him and he was removing dust from his hair (as if he had just returned from the battle). The latter said: You have laid down arms. By God, we haven't (yet) laid them down. So march against them. The Messenger of Allah ﷺ asked: Where? He pointed to Banu Quraiza. So the Messenger of Allah (may peace he upon him) fought against them. They surrendered at the command of the Messenger of Allah ﷺ, but he referred the decision about them to Sa'd who said: I decide about them that those of them who can fight be killed, their women and children taken prisoners and their properties distributed (among the Muslims). (Using translation from Muslim 1769a)
أُصِيبَ سَعْدٌ يَوْمَ الْخَنْدَقِ رَمَاهُ رَجُلٌ مِنْ قُرَيْشٍ يُقَالُ لَهُ حِبَّانُ بْنُ الْعَرِقَةِ فِي الْأَكْحَلِ فَضَرَبَ عَلَيْهِ رَسُولُ اللهِ ﷺ خَيْمَةً فِي الْمَسْجِدِ لِيَعُودَهُ مِنْ قَرِيبٍ