Musnad Ahmad 31:446

'Abd al-Malik narrated to us, Hisham narrated to us, from Zayd, from 'Ata' ibn Yasar, from Abu Sa'id al-Khudri, from the Prophet, peace and blessings of Allah be upon him, who said: "Beware of sitting on the roads." They said: "O Messenger of Allah, we have no alternative to our sittings in which we converse." He said: "Then give the road its right." They said: "And what is the right of the road, O Messenger of Allah?" He said: "Lowering the gaze, refraining from harm, enjoining the good, and forbidding the evil."