Albert Barnes Commentary 1 Samuel 20:19

"And when thou hast stayed three days, thou shalt go down quickly, and come to the place where thou didst hide thyself when the business was in hand, and shalt remain by the stone Ezel." — 1 Samuel 20:19 (ASV)

The stone Ezel - This stone is not mentioned anywhere else, except possibly in 1 Samuel 20:41 (see the note on that verse).