Please allow me to burst this bubble of the so-called son of promise.<quoted text>
That's the only way you can sale your false religion, by trying to discredit the true revelations of God. From the very start islam is based on a falsehood; claiming ishmael and not Isaac was the oblation requested of Abraham by God Himself! islam is a no starter!
Sarah could not conceive for decades. She gave Hagar to Pappy, as a wife, according to the Bible.
Hagar gave pappy a son. Sarah craved for a child. Pappy made love every day. God granted her wish. That is all there is to it. The point is that Issac was also a child of sex and flesh.
No big deal!
Now, was Jesus also a son of promise? Be careful, when you are answer.