Here is a benefit on the Sunnah of greeting a Muslim after being separated by a wall or tree or the likes. Whenever I go downtown, I am reminded of this Hadith because the streets are crowded and we are usually forced to separate with those whom we are walking with either by a tree or pole and then unite again.

عن رسول الله صلى الله عليه وسلم، قال‏:‏ ‏ ‏إذا لقي أحدكم أخاه، فليسلم عليه، فإن حالت بينهما شجرة، أو جدار، أو حجر، ثم لقيه، فليسلم عليه‏

Abu Hurairah (May Allah be pleased with him) reported:

The Messenger of Allah (ﷺ) said, “When one of you meets a brother (in Faith) he should greet him. Then if a tree or a wall or a stone intervenes between them and then he meets him again, he should greet him.”

[Saheeh Sunan Abi Dawood no. 5200]

Shaikh Abdul-Muhsin al-‘Abbad hafidhuhallah said:

“A large rock separates between them. Not a small rock or something descending/downward. It is only something that veils some from the other or distances one from the other like a large rock or something the size of a person or less than that. As for something on the earth and causes a separation, (and) due to this, then this one (individual) walks to the right of the pebbles and that one (other individual walks) to the left (of the pebbles), then this does not need of greeting. This is because it did not cause a separation which distinguishes one from the other. So the intent of rock is a large rock like a wall. Then (the ruling is that if) he meets him again, then he gives him greeting, (and) so (the case has been that) he gives greetings another time. This indicates that a person should repeat the greetings when he leaves and enters (since) separation occurred. When both are walking and are separated by a tree, or wall, or a large rock, or what is like that, then one gives greetings to the other”

[Sharh Sunan Abu Dawood no. 591]

Translated by

Faisal Ibn Abdul Qaadir Ibn Hassan
Abu Sulaymaan