Hadith: The one who is riding should greet the one walking, the one who is walking should greet the one sitting, and the small group of people should greet the large one

عَن أَبِي هُرَيْرَةَ رضي الله عنه قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ:
«يُسَلِّمُ الرَّاكِبُ عَلَى المَاشِي، وَالمَاشِي عَلَى القَاعِدِ، وَالقَلِيلُ عَلَى الكَثِيرِ». وَلِلبُخَارِي: «يُسَلِّمُ الصَّغِيرُ عَلَى الكَبِيرِ، وَالمَارُّ عَلَى القَاعِدِ، وَالقَلِيلُ عَلَى الكَثِيرِ».
[صحيح] - [متفق عليه] - [صحيح البخاري: 6232]

Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said:
"The one who is riding should greet the one walking, the one who is walking should greet the one sitting, and the small group of people should greet the large one."
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 6232]

Explanation

The Prophet (may Allah's peace and blessings be upon him) guides to the etiquette of extending the greeting of peace among people: "As-salāmu ‘alaykum wa rahmatullāhi wa barakātuh" (may the peace, mercy, and blessings of Allah be upon you). The young should greet the old, the one who is riding should greet the one walking, the one who is walking should greet the one sitting, and a small group of people should greet the large one.