The meaning is that the Messenger of Allah ﷺ passed by Hamza, who had been mutilated, and said, "Were it not that Safiyya would feel grief in her heart, I would have left him to be devoured by the beasts and birds, so that he would be resurrected from their bellies."Shrouds were scarce and the slain were many, so one, two, or three men would be wrapped together in a single shroud.Qutayba added, "Then they would be buried together in one grave, and the Messenger of Allah ﷺ would ask which of them had memorized the most Quran, and place him closest to the qiblah."
حدثنا عثمان بن أبي شيبة حدثنا زيد يعني ابن الحباب ح و حدثنا قتيبة بن سعيد حدثنا أبو صفوان يعني المرواني عن أسامة عن الزهري
المعنى أن رسول الله ﷺ مر على حمزة وقد مثل به فقال لولا أن تجد صفية في نفسها لتركته حتى تأكله العافية حتى يحشر من بطونها وقلت الثياب وكثرت القتلى فكان الرجل والرجلان والثلاثة يكفنون في الثوب الواحد زاد قتيبة ثم يدفنون في قبر واحد فكان رسول الله ﷺ يسأل أيهم أكثر قرآنا فيقدمه إلى القبلة
[Its chain of transmission is daif] Tirmidhi narrated it in the Book of Funerals, chapter on what has been said about those killed at Uhud and the mention of Hamza, hadith no. 1016, from Qutayba bin Saeed with this wording, and he said, hasan "ghareeb," and Hakim graded it sahih (3/196), and Dhahabi agreed with him. Zuhri narrated it with an ambiguous form of transmission ("an").