Genesis 39:2

And the LORD was with Joseph, and he was a prosperous man; and he was in the house of his master the Egyptian.

He was in the house of his master. Those slaves who had been war-captives were generally sent to labour in the field, and subjected to hard treatment under the 'stick' of taskmasters. But those who were bought with money were employed in domestic purposes, were kindly treated, and enjoyed as much liberty as the same class does in modern Egypt.