'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. But the Lord was with Joseph, and showed him mercy, and gave him favour in the sight of the keeper of the prison. And the keeper of the prison committed to Joseph's hand all the prisoners that were in the prison; and whatsoever they did there, he was the doer of it. The keeper of the prison looked not to any thing that was under his hand; because the Lord was with him, and that which he did, the Lord made it to prosper.'--GENESIS xxxix. 20-23.
'And it came to pass after these things, that the butler of the king of Egypt and his baker had offended their lord the king of Egypt. And Pharaoh was wroth against two of his officers, against the chief of the butlers, and against the chief of the bakers. And he put them in ward in the house of the captain of the guard, into the prison, the place where Joseph was bound. And the captain of the guard charged Joseph with them, and he served them: and they continued a season in ward. And they dreamed a dream both of them, each man his dream in one night, each man according to the interpretation of his dream, the butler and the baker of the king of Egypt, which were bound in the prison. And Joseph came in unto them in the morning, and looked upon them, and, behold, they were sad. And he asked Pharaoh's officers that were with him in the ward of his lord's house, saying, Wherefore look ye so sadly to day? And they said unto him, We have dreamed a dream, and there is no interpreter of it. And Joseph said unto them, Do not interpretations belong to God? tell me them, I pray you. And the chief butler told his dream to Joseph, and said to him, In my dream, behold, a vine was before me; And in the vine were three branches: and it was as though it budded, and her blossoms shot forth; and the clusters thereof brought forth ripe grapes: And Pharaoh's cup was in my hand: and I took the grapes, and pressed them into Pharaoh's cup, and I gave the cup into Pharaoh's hand. And Joseph said unto him, This is the interpretation of it: The three branches are three days: Yet within three days shall Pharaoh lift up thine head, and restore thee unto thy place: and thou shalt deliver Pharaoh's cup into his hand, after the former manner when thou wast his butler. But think on me when it shall be well with thee, and shew kindness, I pray thee, unto me, and make mention of me unto Pharaoh, and bring me out of this house: For indeed I was stolen away out of the land of the Hebrews: and here also have I done nothing that they should put me into the dungeon.'--GENESIS xl. 1-15.
Potiphar was 'captain of the guard,' or, as the title literally runs, chief of the executioners. In that capacity he had charge of the prison, which was connected with his house (Gen. xl. 3). It is, therefore, quite intelligible that he should have put Joseph in confinement on his own authority, and the distinction drawn between such a prisoner and the 'king's prisoners,' who were there by royal warrant or due process of law, is natural. Such high-handed treatment of a slave was a small matter, and it was merciful as well as arrogant, for death would have been the punishment of the crime of which Joseph was accused. Either Potiphar was singularly lenient, or, as is perhaps more probable, he did not quite believe his wife's story, and thought it best to hush up a scandal. The transfer of Joseph from the house to the adjoining prison would be quietly managed, and then no more need be said about an ugly business.