Genesis 15:7-8

"And he said unto him, I am Jehovah that brought thee out of Ur of the Chaldees, to give thee this land to inherit it. And he said, O Lord Jehovah, whereby shall I know that I shall inherit it?"

Significantly, (1) Jehovah (by that name) is already known to Abram; (2) also, the covenant is already in existence (Genesis 12:1ff); and what the narrative here is concerned with is the question of Abram as to how he could know that it would really be fulfilled.