'Abdu'r-Rahman ibn Shibl said that he heard the Prophet, may Allah bless him and grant him peace, said, "The person riding should greet the person on foot. The person on foot should greet the person who is seated. The smaller group should greet the large. Whoever answers the greeting, that is for him. Whoever does not answer it, has nothing."  

سَمِعْتُ النَّبِيَّ ﷺ يَقُولُ لِيُسَلِّمِ الرَّاكِبُ عَلَى الرَّاجِلِ وَلْيُسَلِّمِ الرَّاجِلُ عَلَى الْقَاعِدِ وَلْيُسَلِّمِ الأَقَلُّ عَلَى الأَكْثَرِ فَمَنْ أَجَابَ السَّلاَمَ فَهُوَ لَهُ وَمَنْ لَمْ يُجِبْ فَلا شَيْءَ لَهُ  

Abu Hurayra reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "The person riding greets the person walking. The person walking greets the person sitting. The small group greets the large group."  

عَنْ رَسُولِ اللهِ ﷺ قَالَ يُسَلِّمُ الرَّاكِبُ عَلَى الْمَاشِي وَالْمَاشِي عَلَى الْقَاعِدِ وَالْقَلِيلُ عَلَى الْكَثِيرِ  

Jabir said, "When two people walking meet, then the one who gives the greeting first is the better of them."  

أَنَّهُ سَمِعَ جَابِرًا يَقُولُ الْمَاشِيَانِ إِذَا اجْتَمَعَا فَأَيُّهُمَا بَدَأَ بِالسَّلاَمِ فَهُوَ أَفْضَلُ