Musnad Ahmad 962:121

'Abd al-Rahman narrated to us, from Mu'awiyah ibn Salih, from Sulaym ibn 'Amir al-Kala'i, who said: I heard Abu Umamah say: I heard the Messenger of Allah (peace and blessings of Allah be upon him) while he was on that day upon al-Jad'a' (his she-camel), placing his feet in the stirrups, stretching himself to be heard by the people. He said at the top of his voice: "Do you not hear?" A man from among the groups of people said: O Messenger of Allah, what do you enjoin upon us? He said: "Worship your Lord, pray your five (prayers), fast your month, and obey those in authority over you; you will enter the Paradise of your Lord." I said: O Abu Umamah, how old were you on that day? He said: I was on that day thirty years old, jostling the camel, pushing it forward for the Messenger of Allah (peace and blessings of Allah be upon him).