Musnad Ahmad 658:16

'Affan narrated to us, Shu'bah narrated to us, Abu Ishaq informed us, from Al-Bara', (Shu'bah said: And he did not hear it from Al-Bara'), that the Messenger of Allah (peace and blessings of Allah be upon him) passed by some people of the Ansar and said: "If you must do so, then spread the greeting of peace, help the oppressed, and guide the way."