Where the king's prisoners were bound — Potiphar, it is likely, chose that prison because it was the worst; for there the irons entered into the soul, Psalms 105:18, but God designed it to pave the way to his enlargement. Our Lord Jesus, like Joseph was bound, and numbered with the transgressors.
Related Commentaries of Genesis 39:20
Genesis 39:20
20 And Joseph's master took him, and put him into the prison, a place where the king's prisoners were bound: and he was there in the prison.