Musnad Abu Ya'la al-Mawsili 3:28

Zuhayr narrated to us, Abd al-Rahman ibn Mahdi narrated to us, Shu'bah narrated to us, from Muhammad ibn al-Munkadir, who said: I heard Mas'ud ibn al-Hakam narrating from Ali, who said: We saw the Messenger of Allah (may Allah bless him and grant him peace) stand, so we stood, and he sat, so we sat; meaning regarding the funeral.