Musannaf Ibn Abi Shayba 6:441

Ibn Fudayl narrated to us, from Yahya al-Jabir, from Abu Majid, who said: I asked Ibn Mas’ud about walking with the funeral procession. He said: The walking is at a pace less than a trot. Indeed, the funeral procession is followed and does not follow; there is no one with it who precedes it.