«إذا اصطحب رجلان مسلمان فحال بينهما شجر أو حجر أو مدر فليسلم أحدهما على الآخر ويتباذلوا السلام»
The Prophet (peace and blessings be upon him) said:
"When two Muslim men are walking together and a tree, a stone or a clod of earth comes between them (and they separate and then meet again), then one of them should greet the other with salam, and they should exchange greetings of salam with each other."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 355