And not being weak in faith, he did not consider his own body, already dead (since he was about a hundred years old), and the deadness of Sarah’s womb. He did not waver at the promise of God through unbelief, but was strengthened in faith, giving glory to God, and being fully convinced that what He had promised He was also able to perform.
- Romans 4:19–21
Let us hold fast the confession of our hope without wavering, for He who promised is faithful.
- Hebrews 10:23

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

Now faith is the substance of things hoped for, the evidence of things not seen.
- Hebrews 11:1
So shall My word be that goes forth from My mouth; it shall not return to Me void, but it shall accomplish what I please, and it shall prosper in the thing for which I sent it.
- Isaiah 55:11