In Genesis it saws “So Abraham prayed to God; and God healed Abimelech, his wife, and his female servants. Then they bore children;” (Genesis 20:17)
In the first book of the Bible, Genesis, we have the story of Abraham. In this passage Abraham prayed to God and believed that God would bring a miracle, a child in their old age just as God had promised. The writer of Hebrews in the New Testament also mentions this point where it saws By faith Sarah herself also received strength to conceive seed, and she bore a child when she was past the age, because she judged Him faithful who had promised (Hebrews 11:11). So today like Abraham we can look at God as One that is faithful. What He promised about Abraham and Sarah having a son, He fulfilled. So what God has promised us, He will fulfill, we just need to pray, believe Him, trust Him, obey Him and wait for His timing.