Musnad Ahmad 31:596

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Zayd ibn Aslam, from a man, from Abu Sa'id, that the Prophet, peace and blessings of Allah be upon him, said: "Beware of sitting on the roads." Ma'mar perhaps said: "On the pathways." They said: "O Messenger of Allah, we have no choice but to use our sitting places." He said: "Then give them their right." They said: "And what is their right?" He said: "Returning the greeting, lowering the gaze, guiding the seeker, enjoining the good, and forbidding the evil."