Genesis 27:32

And Isaac his father said unto him, who [art] thou?.... Hearing another voice more like Esau's than what he had heard before surprised him, and therefore in haste puts this question:

and he said, I [am] thy son, thy firstborn Esau; all which was true in a sense; he was his son, and he was Esau, and he was his firstborn by nature, but not by right, for he had sold his birthright.