And he gave him the covenant of circumcision: and so (Abraham) begat Isaac, and circumcised him the eighth day; and Isaac (begat) Jacob, and Jacob the twelve patriarchs.
For it is written, that Abraham had two sons, one by the handmaid, and one by the freewoman.
By faith even Sarah herself received power to conceive seed when she was past age, since she counted him faithful who had promised:
But my covenant will I establish with Isaac, whom Sarah shall bear unto thee at this set time in the next year.