Musnad Ahmad 788:219

Abu al-Nadr narrated to us, he said: Abu Mu’awiyah—meaning Shayban—narrated to us, from Layth, from Abu Burdah ibn Abi Musa, from his father, from the Prophet (peace and blessings of Allah be upon him), who said: "If a funeral passes by you, then whether it is a Muslim, a Jew, or a Christian, stand up for it; for it is not for it that we stand, but we stand for those who are with it from among the angels." Layth said: I mentioned this hadith to Mujahid, and he said: Abdullah ibn Sakhbarah al-Azdi narrated to me, saying: We were sitting with Ali (may Allah be pleased with him) waiting for a funeral, when another one passed by us, so we stood up. Ali (may Allah be pleased with him) said: "What makes you stand?" We said: "This is what you bring to us, O companions of Muhammad." He said: "And what is that?" I said: "Abu Musa claimed that the Messenger of Allah (peace and blessings of Allah be upon him) said: 'If a funeral passes by you, whether it is a Muslim, a Jew, or a Christian, stand up for it; for it is not for it that we stand, but we stand for those who are with it from among the angels.'" Ali (may Allah be pleased with him) said: "The Messenger of Allah (peace and blessings of Allah be upon him) never did that except once for a man from the Jews. They were People of the Book, and he used to imitate them, but when he was forbidden, he stopped, and he never returned to it after that."