Romans 4:18-22

Against all hope Abraham in hope trusted God, so he could become the father of many peoples, just as God had promised him: “This is how many descendants you'll have!” His trust in God didn't weaken even though he thought his body was practically dead (he was around a hundred years old), and knew that Sarah was too old to have children. He held on to God's promise—he didn't doubt it. Instead his trust in God grew stronger, and he gave glory to God. He was totally convinced that what God had promised he had the power to deliver. That's why Abraham was considered right by God.