Musannaf Ibn Abi Shaybah 12267 — Those who said one stands

Sayyiduna Amir bin Rabi'ah (may Allah be pleased with him), tracing it back to the Prophet (peace and blessings be upon him), narrated that he (peace and blessings be upon him) said: "When you see a funeral passing, stand up until it leaves you behind (and goes ahead) or it is put down."