(453) بَابُ يُسَلِّمُ الْمَاشِي عَلَى الْقَاعِدِ
'Abdu'r-Rahman ibn Shibl said that he heard the Prophet, may Allahbless him and grant him peace, said, "The person riding should greet theperson 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."
Reference: Al-Adab Al-Mufrad 992
In-book reference: Book 42, Hadith 28
English translation: Book 42, Hadith 992