Saad bin Muaz was struck by an arrow on the Day of the Confederates, which severed his median vein, or perhaps his arm vein. The Messenger of Allah ﷺ cauterized the wound with fire, but his hand swelled up, so he left it. The blood then flowed freely, so he cauterized it a second time, and again his hand swelled.When Saad saw this, he said, "O Allah, do not let my soul depart until You have given my eyes the satisfaction of seeing what becomes of Banu Qurayza."His vein then held back, and not a single drop fell, until they came down to accept the judgment of Saad bin Muaz. The Messenger of Allah ﷺ sent for him, and he ruled that their men be killed and their women spared so that the Muslims could make use of them.The Messenger of Allah ﷺ said, "You have judged according to the ruling of Allah concerning them."They numbered four hundred. When the killing of them was completed, Saad's vein burst open and he died.
رمي يوم الأحزاب سعد بن معاذ فقطعوا أكحله- أو أبجله- فحسمه رسول الله ﷺ بالنار، فانتفخت يده، فتركه فنزفه الدم، فحسمه أخرى فانتفخت يده، فلما رأى ذلك قال: اللهم لا تخرج نفسي حتى تقر عيني من بني قريظة، فاستمسك عرقه، فما قطر قطرة، حتى نزلوا على حكم سعد بن معاذ. فأرسل إليه، فحكم أن يقتل رجالهم وتستحيى نساؤهم، يستعين بهن المسلمون، فقال رسول الله ﷺ: أصبت حكم الله فيهم وكانوا أربعمائة، فلما فرغ من قتلهم انفتق عرقه فمات.
Narrated by Tirmidhi (1582), Ahmad (14773), and Ibn Hibban (4784), all through chains from Layth bin Saad, from Abu Zubayr, from Jabir, who said, and then he related it. Its chain of transmission is sahih, and Tirmidhi said, hasan sahih. Hafiz also declared its chain sahih in Fath al-Bari (7/414).This hadith establishes that those killed on the day of Qurayza numbered four hundred. The scholars of military campaigns and biography differed over their number, with some going up to nine hundred, but the correct account is what is found in Jabir's hadith. Some have reconciled this by saying that the number Jabir mentioned refers to the fighters, while the rest were their followers.This is the fate of anyone who betrays his homeland and breaks his covenant, because the security of the state comes before all else. These traitors had put the city of the Prophet ﷺ and the Muslims in grave danger, so Allah granted the believers victory over their enemies by having their men killed and their women taken captive, and with this the looming danger surrounding the Islamic state came to an end. It is said that they were brought into Madinah, a trench was dug for them in the marketplace, and they were beheaded there.