Genesis 39:5 And it came to pass from the time that he had made him overseer in his house, and over all that he had, that the LORD blessed the Egyptian's house for Joseph's sake; and the blessing of the LORD was upon all that he had in the house, and in the field. - Free Bible Online

      5. the Lord blessed the Egyptian's house for Joseph's sake, &c.--It might be--it probably was--that a special, a miraculous blessing was poured out on a youth who so faithfully and zealously served God amid all the disadvantages of his place. But it may be useful to remark that such a blessing usually follows in the ordinary course of things; and the most worldly, unprincipled masters always admire and respect religion in a servant when they see that profession supported by conscientious principle and a consistent life.
      made him overseer in his house--We do not know in what capacity Joseph entered into the service of Potiphar; but the observant eye of his master soon discovered his superior qualities and made him his chief, his confidential servant (compare Eph 6:7; Col 3:23). The advancement of domestic slaves is not uncommon, and it is considered a great disgrace not to raise one who has been a year or two in the family. But this extraordinary advancement of Joseph was the doing of the Lord, though on the part of Potiphar it was the consequence of observing the astonishing prosperity that attended him in all that he did.

JFB.