وَعَنْ عَلِيٍّ رضى الله عنه
قَالَ: قَالَ رَسُولُ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ -«يُجْزِئُ عَنْ اَلْجَمَاعَةِ إِذَا مَرُّوا أَنْ يُسَلِّمَ أَحَدُهُمْ، وَيُجْزِئُ عَنْ اَلْجَمَاعَةِ أَنْ يَرُدَّ أَحَدُهُمْ»
“When a group of people passes by, it is sufficient if one of them gives a salutation, and it is sufficient for those who are sitting that one of them replies.” Related by Ahmad and Al-Baihaqi.
Bulugh al-Maram 1643, Book 16, The Comprehensive Book, Hadith 9. 1 min read