John Calvin Commentary Genesis 39:20

"And Joseph`s master took him, and put him into the prison, the place where the king`s prisoners were bound: and he was there in the prison." — Genesis 39:20 (ASV)

And put him into the prison. Though Moses does not state with what degree of severity Joseph was afflicted at the beginning of his imprisonment, yet we readily gather that he was not allowed any liberty, but was thrust into some obscure dungeon. The authority of Potiphar was paramount; he had the keeper of the prison under his power, and at his disposal. What clemency could be hoped for from a man who was jealous and carried away with the vehemence of his anger? There is no doubt that what is related of Joseph in Psalm 105:18,

His feet were made fast in fetters, and the iron entered into his soul,

had been handed down by tradition from the fathers. What a reward of innocence! For, according to the flesh, he might ascribe whatever he was suffering to his integrity. Truly, in this temptation he must have mourned in great perplexity and anxiety before God. And though Moses does not record his prayers, yet, since it is certain that he was not crushed beneath the cross, and did not murmur against it, it is also probable that he was resting on the hope of Divine help. And to flee to God is the only stay that will support us in our afflictions, the only armor that renders us invincible.