Musnad Ahmad 626:29

'Abd al-Wahid al-Haddad narrated to us, Sa'id ibn 'Ubayd Allah al-Thaqafi narrated to us, from Ziyad ibn Jubayr, from al-Mughirah ibn Shu'bah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The rider is behind the funeral procession, and the walker is wherever he wishes from it, and the child—the funeral prayer is performed over him."