Refusing Potiphar's wife, Joseph asked how he could do such evil and sin against whom?

Answer: God

Potiphar had withheld nothing from Joseph except his wife. "How could I do such a great evil and sin against God?" Joseph asked.

“No one in this house is greater than I am. He has withheld nothing from me except you, because you are his wife. So how could I do such a great evil and sin against God?””— Genesis 39:9 (BSB)