Musnad Abu Ya'la al-Mawsili 3:310

Ubayd Allah narrated to us, Abd al-Rahman narrated to us, Shu'bah narrated to us, from Muhammad ibn al-Munkadir, from Mas'ud ibn al-Hakam, 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 at the funeral.