All of them mentioned that they heard Zuhri narrate that Salim informed him that his father informed him that he saw the Prophet ﷺ, Abu Bakr, Umar, and Uthman walking in front of the funeral procession. Bakr alone did not mention Uthman.Abu Abdul-Rahman said, "This is a mistake, and the correct version is mursal."
أخبرنا محمد بن عبد الله بن يزيد قال حدثنا أبي قال حدثنا همام قال
كلهم ذكروا أنهم سمعوا من الزهري يحدث أن سالما أخبره أن أباه أخبره أنه رأى النبي ﷺ وأبا بكر وعمر وعثمان يمشون بين يدي الجنازة بكر وحده لم يذكر عثمان قال أبو عبد الرحمن هذا خطأ والصواب مرسل
[Its isnad is hasan] Tirmidhi narrated it, no. 1007, from the hadith of Hammam bin Yahya, through him (see the previous hadith), and it is also in Kubra, no. 2072. The hadith has corroborating narrations, and the criticism raised by Hafiz Nasai, may Allah have mercy on him, is outweighed and does not constitute a defect that invalidates the hadith.