It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that a man asked the Noble Prophet (peace and blessings be upon him): "Which deed is the best?" He (peace and blessings be upon him) replied: "That you feed others and greet everyone, whether you know them or not."
Hadith Takhrij«أخرجه البخاري12، 28، 6236، ومسلم: 39 ، (انظر مسند أحمد ترقيم الرسالة: 6581 ترقیم بيت الأفكار الدولية: 6581»
Brief Explanation
Benefits: ... The basis for honoring a guest should not be personal acquaintance, as has become the attitude of most people. Nowadays, only two things are given preference: one is personal acquaintance and the other is wealth. If a guest does not possess these two qualities, even exchanging greetings with him is not considered tolerable. This distinction is the result of being distant from Islamic teachings.