Genesis 26:2-6

And the Lord appeared to him and said, “Do not go down to Egypt; stay in the land of which I shall tell you.

Live for a time in this land and I will be with you and bless you, for to you and to your descendants I will give all these lands, and I will establish the oath which I swore to your father Abraham.

I will multiply your descendants as the stars of heaven, and will give your descendants all these lands; and by your descendants all the nations of the earth shall be blessed,

because Abraham obeyed Me and fulfilled his duty to Me, and kept My commandments, My statutes, and My laws.”

So Isaac lived in Gerar.