Ali bin Abi Talib (may Allah be pleased with him) narrates: When a group of people passes by, it is sufficient for one person among them to give the greeting (salaam), and for those who are sitting, it is sufficient for one person among them to reply. Baihaqi narrated it as marfu’ in Shu’ab al-Iman. And Abu Dawood, after narrating this hadith, said: Hasan bin Ali narrated it as marfu’, and he is a teacher of Abu Dawood. Hasan, narrated by al-Bayhaqi in Shu’ab al-Iman and Abu Dawood.