Saad was wounded on the day of the Trench when a man from Quraysh shot him with an arrow that struck the median vein of his arm. The Messenger of Allah ﷺ pitched a tent for him in the mosque so that he could visit him from close by.
أخبرنا عبيد الله بن سعيد قال حدثنا عبد الله بن نمير قال حدثنا هشام بن عروة عن أبيه
أصيب سعد يوم الخندق رماه رجل من قريش رمية في الأكحل فضرب عليه رسول الله ﷺ خيمة في المسجد ليعوده من قريب
Bukhari transmitted it, Prayer, chapter on setting up a tent in the masjid for the sick and others, no. 463, and Muslim, Jihad and Expeditions, chapter on the permissibility of fighting one who breaks a covenant, no. 65/1769, from the hadith of Ibn Numayr through this chain, and it is also found in Kubra, no. 789.