Abu Maryam reported from Abu Hurayrah that he heard him say:
He who meets his brother then let him send Salam upon him (give him Salam), if a tree or wall comes between them then he meets him again let him send Salam upon him (give him Salams)
Ash Shaykh Abdurrazaaq al Badr said:
This is a Sunnah which many of the people are heedless from, either that they don’t know of it or that they don’t pay concern with applying it.
I remember when I was young in age and Beside Ash Shaykh Albani Rahimahullah here in Madeenah and I was waking by his side alone. A pillar separated between me and him thus when he met me after the pillar he turned to me smiling and said 
السلام عليكم
I said 
وعليكم السلام 
He said: “Why did I give you Salams”
I didn’t know this narration nor was I previously aware of it 
I smiled and said to him because the Salam is good 
And he mentioned to me this narration
Thus my first time becoming aware of this narration was from the Shaykh Rahimahullah 
Explanation of Adab al Mufrad tape 133