It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him), he said: When one meets his Muslim brother, he should greet him with salam. If a tree or a wall comes between them and then they meet again, he should greet him with salam again.
Hadith Referenceالادب المفرد / كتاب السلام / 1010
Hadith Gradingالألبانی:صحيح موقوفًا و صح مرفوعًا
Hadith Takhrij«صحيح موقوفًا و صح مرفوعًا : سنن أبى داؤد ، الأدب ، حديث : 5200»
Explanation & Benefits
Shaykh Maulana Usman Muneeb
Benefits and Issues: This narration is authentic both as a marfu‘ (attributed to the Prophet sallallahu alayhi wa sallam) and as a mawquf (attributed to the Companion). From this, the importance of the greeting of salam and the manner of spreading it generally is understood, showing how significant it is.
Source: Fadlullah al-Ahad: Urdu Commentary on al-Adab al-Mufrad, Page: 1010