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.
All Commentaries on Genesis 39:20 Go To Genesis 39
Ambrose of Milan
AD 397
Therefore I might say Joseph was happier when he was put into prison, because he was giving witness on behalf of chastity. For modesty is a good gift but one of lesser merit when it involves no risk. Where, however, it is maintained at the risk of one’s safety, there it wins a more abundant crown. With his case unheard, his truthfulness unexamined, Joseph is sent into prison as if guilty of a crime. But the Lord did not abandon him even in prison. The innocent should not be troubled when they are attacked on false charges, when justice is overcome and they are shoved into prison. God visits his own even in prison, and so there is more help for them there, where there is more danger.