John Gill Commentary 1 Samuel 26:3

"And Saul encamped in the hill of Hachilah, which is before the desert, by the way. But David abode in the wilderness, and he saw that Saul came after him into the wilderness." — 1 Samuel 26:3 (ASV)

And Saul pitched in the hill of Hachilah, which [is] before
Jeshimon, by the way
To the wilderness; the very same place where the Ziphites suggested David was:

but David abode in the wilderness ;
not in the hill of Hachilah, but in the wilderness of Ziph itself:

and he saw that Saul came after him into the wilderness ;
he understood, by some information he had, that Saul had set out from Gibeah, and was coming to seek for him in the wilderness of Ziph; perhaps Jonathan had given him intelligence; however, he was not quite certain, as appears by what follows.