It is narrated from Sayyiduna Abu Shurayh bin Amr al-Khuza'i (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Beware of sitting on the roads; yet if any of you does sit on the road, let him give it its due." We said: O Messenger of Allah, what is its due? He (peace and blessings be upon him) said: "Lowering the gaze, returning greetings, enjoining good, and forbidding evil."
Hadith Referenceالمعجم الكبير للطبراني / باب الهاء / 18708