Saad was wounded on the day of the Trench when a man from Quraysh named Hibban bin al-Ariqah shot him in the median vein. The Prophet ﷺ pitched a tent for him in the mosque so he could visit him from nearby. His wound continued to flow with blood until he died from it.
أصيب سعد يوم الخندق، رماه رجل من قريش يقال له: حبان بن العرقة رماه في الأكحل فضرب النبي ﷺ خيمة في المسجد ليعوده من قريب إلا أن جرحه يغذو دما فمات منها.
Bukhari narrated it in Maghazi (4122) and Muslim in Jihad (1769), both from the hadith of Abdullah bin Numayr, who said, "Hisham narrated to us, from his father, from Ayesha," and he mentioned it in a longer hadith as will come later, and that he died about twenty-five nights after the departure of the Confederates, and after he had passed judgment concerning Banu Qurayza.Musa bin Uqba narrated from Ibn Shihab, regarding the naming of those from the Ansar who were martyred on the day of the Trench, Anas bin Muaz bin Aws bin Abdu Amr. Tabarani narrated it in Kabir (1/238), and it is mursal.The authors of sira and maghazi mentioned among those martyred on the day of the Trench, Abdullah bin Sahl al-Ashhali, Thalaba bin Ghanama bin Adi al-Ansari al-Khazraji, Tufayl bin Numan al-Ansari, Kaab bin Zayd al-Ansari al-Bukhari, Sulayt bin Awf al-Aslami, Sufyan bin Awf al-Aslami, and Sinan bin Sayfi al-Khazraji, though there is disagreement regarding some of them.