It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that a man asked the Messenger of Allah (peace and blessings be upon him): "What is the best form of Islam?" He (peace and blessings be upon him) replied: "That you feed (others), and greet with salam both those you know and those you do not know."
Hadith Referenceالادب المفرد / كتاب السلام / 1050
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : صحيح البخاري ، الإيمان ، حديث : 12»
Explanation & Benefits
Shaykh Maulana Usman Muneeb
Benefits and Issues: It is not necessary for a person to be acquainted with another in order to offer salam; rather, it is obligatory to greet every Muslim with salam. Further details have already been discussed in the previous pages.
Source: Fadlullah al-Ahad: Urdu Commentary on al-Adab al-Mufrad, Page: 1050