Silsilat al-Ahadith al-Sahihah

Sayyiduna Abdur Rahman bin Shibl (may Allah be pleased with him) says that I heard the Messenger of Allah (peace and blessings be upon him) say: "The rider should greet the one who is walking, the one who is walking should greet the one who is sitting, and those who are fewer in number should greet those who are greater in number. Whoever responds to the greeting will receive a reward, and whoever does not respond will be deprived of the reward."