Genesis 15:6
4 But look, the Lord’s message came to him: “This man will not be your heir, but instead a son who comes from your own body will be your heir.” 5 The Lord took him outside and said, “Gaze into the sky and count the stars—if you are able to count them!” Then he said to him, “So will your descendants be.” 6 Abram believed the Lord, and the Lord credited it as righteousness to him.
Isaiah 40:26
25 “To whom can you compare me? Whom do I resemble?” says the Holy One. 26 Look up at the sky! Who created all these heavenly lights? He is the one who leads out their ranks; he calls them all by name. Because of his absolute power and awesome strength, not one of them is missing. 27 Why do you say, Jacob, Why do you say, Israel, “The Lord is not aware of what is happening to me; my God is not concerned with my vindication”?
Notes and References
"... God responds to Abraham's lament by promising a son of his own body, reinforcing this promise with a sign; in fact, however, the sign, the countless stars, is an extension of the promise of a son to include the promise of many descendants; it presupposes the combination of the two. It is precisely the promise of many descendants, cast in this lovely form, that is meant to speak to the Israelites in their days of peril. It is a revitalization of the promise of increase, which has set its indelible stamp on the endangered nation. Thus, the ancient promise to Abraham lives on in a changed situation. There is a clear echo of Deutero-Isaiah's message during the Exile (Isaiah 40:26): he also calls on his hearers to look up at the stars. In both passages, it is an awareness of the broad arena within which the Creator works that is contrasted to oppressive suffering ..."
Westermann, Claus and David Green Genesis (p. 119) T&T Clark International, 2004