On the day of Uhud, I saw two men in white garments to the right and left of the Messenger of Allah ﷺ, fighting on his behalf as fiercely as could be. I had never seen them before, nor did I see them afterward.
حدثنا سليمان بن داود الهاشمي أنبأنا إبراهيم بن سعد عن أبيه عن أبيه
لقد رأيت عن يمين رسول الله ﷺ وعن يساره يوم أحد رجلين عليهما ثياب بيض يقاتلان عنه كأشد القتال ما رأيتهما قبل ولا بعد
Its isnad is sahih. "From his father, from his father" means that Ibrahim bin Saad narrates it from his father Saad bin Ibrahim, and his father Saad narrates it from his father Ibrahim bin Abdul-Rahman bin Awf, and Ibrahim bin Abdul-Rahman narrates it from Saad bin Abu Waqqas. The two Shaikhs (Bukhari and Muslim) narrated this hadith, as noted in Dhakhair Mawarith 2055, and it will come again at 1471.