It is narrated from Sayyiduna Fadala (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: "The rider should greet the one who is walking, and those who are fewer in number should greet those who are greater in number."
Hadith Referenceالادب المفرد / كتاب السلام / 996
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : جامع الترمذي ، الاسئتذان و الآداب ، ح : 2705»
Explanation & Benefits
Shaykh Maulana Usman Muneeb
Benefits and Issues: From these narrations, it is understood that a rider should greet (say salam to) one who is standing or sitting, as well as to one who is walking on foot.
Source: Fadlullah al-Ahad: Urdu Commentary on al-Adab al-Mufrad, Page: 996