Hadis al-Rasool ﷺ

The Prophet (peace and blessings of Allah be upon him) said: "The younger should greet the older, the one who is walking should greet those who are sitting, and the smaller group should greet the larger group." (Because they are fewer in number, they are of lesser status, so they should greet the larger group.) (Tuhfat-ul-Qari)