The young should salute the old, the one who is passing by should salute the one who is sitting, and a small company should salute a large one.
Sunan Abi Dawud Book 43, Hadith 426
← Previous Hadith The Prophet (ﷺ) said: Those who are nearest to Allah are they who are first to give a salutation.

Sunan Abi Dawud Book 43, Hadith 425 Next Hadith → one who is riding should salute one who is walking. He then mentioned the rest of the tradition.

Sunan Abi Dawud Book 43, Hadith 427