Hadith 16:9
Ali (RAA) narrated that the Messenger of Allah (ﷺ) said:
“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.
وَعَنْ عَلِيٍّ - رضى الله عنه - قَالَ: قَالَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -{ يُجْزِئُ عَنْ اَلْجَمَاعَةِ إِذَا مَرُّوا أَنْ يُسَلِّمَ أَحَدُهُمْ, وَيُجْزِئُ عَنْ اَلْجَمَاعَةِ أَنْ يَرُدَّ أَحَدُهُمْ } رَوَاهُ أَحْمَدُ, وَالْبَيْهَقِيُّ