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 begat the twelve patriarchs.
For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.
Through faith also Sara herself received strength to conceive seed, and was delivered of a child when she was past age, because she judged him faithful who had promised.
But my covenant will I establish with Isaac, which Sarah shall bear unto thee at this set time in the next year.