Musnad Ahmad 31:319

'Abd al-Rahman narrated to us, Zuhayr ibn Muhammad narrated to us, from Zayd ibn Aslam, from 'Ata' ibn Yasar, from Abu Sa'id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Beware of sitting in the pathways." They said: "O Messenger of Allah, we have no choice regarding our sittings in which we converse." He said: "If you must sit, then give the path its right." They said: "O Messenger of Allah, and what is the right of the path?" He said: "Lowering the gaze, refraining from harm, returning the greeting, enjoining the good, and forbidding the evil."