Abu Qasim ﷺ said, "By the One in whose hand is the soul of Muhammad, if you knew what I know, you would weep much and laugh little."
حدثنا يزيد أخبرنا محمد بن إسحاق عن أبي الزناد عن الأعرج
أبو القاسم ﷺ والذي نفس محمد بيده لو تعلمون ما أعلم لبكيتم كثيرا ولضحكتم قليلا
Its isnad is sahih. Bukhari 11:459 narrated it through the route of Mamar from Hammam, from Abu Hurairah. Bukhari also narrated it, 11:273, through the route of Zuhri from Ibn Musayab, and Tirmidhi, 3:259–260, through the route of Muhammad bin Amr, from Abu Salama, both of them from Abu Hurairah, as a marfu narration, "If you knew..." without the oath at the beginning.Tirmidhi said, this is a sahih hadith. This hadith has come down from Abu Hurairah through many routes, both at length and in summary form. See, for example, Sahih Ibn Hibban, in our edition, 113, and al-Musnad, 10030, and al-Fath, 11:257.