The rider should first greet the pedestrian, and the pedestrian the one who is seated and a small group should greet a larger group (with as-Salam-u-'Alaikum).
Sahih Muslim Book 39, Hadith 1
← Previous Hadith This hadith has been narrated on the authority of Yunus through another chain of transmitters.

Sahih Muslim Book 38, Hadith 60 Next Hadith → While we were sitting in front of the houses and talking amongst ourselves, Allah's Messenger (ﷺ) happened to come there. He stood by us and said: What about you and your meetings on the paths? Avoid these meetings on the paths. We said: We were sitting here without (any intention of doing harm to the passers-by) ; we are sitting to discuss matters and to hold conversation amongst ourselves. Thereupon he said: If there is no help (for you but to sit on these paths), then give the paths their rights and these are lowering of the gaze, exchanging of greetings and good conversation.

Sahih Muslim Book 39, Hadith 2