Silsilah as-Sahihah 2638 — Etiquette of Salam

Sayyiduna Fadala bin Ubaid (may Allah be pleased with him) narrates that the Noble Prophet (peace and blessings of Allah be upon him) said: "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 few in number should greet those who are greater in number."