John Gill Commentary Numbers 20:23

"And Jehovah spake unto Moses and Aaron in mount Hor, by the border of the land of Edom, saying," — Numbers 20:23 (ASV)

And the Lord spoke unto Moses and Aaron in Mount Hor
When they were at the foot of that mountain, in the valley adjoining to it:

by the coast of the land of Edom ;
which they were still upon the borders of, and were going round it, not being permitted to go through it:

saying ;
as follows.