Musnad Ahmad 33:476

Yunus narrated to us, Aban—meaning al-Attar—narrated to us, from Yahya ibn Abi Kathir, from Ubayd Allah ibn Miqsam, from Jabir ibn Abd Allah, who said: While we were with the Messenger of Allah, may Allah bless him and grant him peace, a funeral procession passed by. We went to carry it, but it turned out to be the funeral of a Jew—or a Jewess. We said: "O Messenger of Allah, it was only the funeral of a Jew—or a Jewess." The Messenger of Allah, may Allah bless him and grant him peace, said: "Death is a source of alarm; so when you see a funeral, stand up."