Genesis 15:5

To the promise of descendants as innumerable as the dust (physical descendants from the land? cf. Genesis 13:16) God added another promise that Abram’s seed would be as countless as the stars. This is perhaps a promise of Abram’s spiritual children, those who would have faith in God as he did. Abram may not have caught this distinction since he would have more naturally taken the promise as a reference to physical children.