Moses Maimonides

“ This verse suggests that Isaac holds a primary position and Ishmael a subordinate place. This point is made even more explicit in the blessing which ignores Ishmael entirely. "For in Isaac shall seed be called in thee." (Genesis 21:12) . The meaning of God's promise to Abraham is that the issue of Ishmael will be vast in numbers but neither pre-eminent nor the object of divine favor, nor distinguished for the attainment of excellence. Not because of them will Abraham be famed or celebrated, but by the noted and illustrious scions of Isaac. ”

“ If he finds it impossible to leave that locality for the time being, he must not become careless and indulge with abandon in the desecration of the Sabbath and the dietary laws on the assumption that he is exempt from all religious obligations. It is the eternally inescapable duty, willy-nilly, of every one belonging to the stock of Jacob to abide by the Law. ”

“ Were there any allusion in the verse to Mohammed, then it would have read "and I shall bless him bimeod meod," and whoever likes to hang on to a spider's web might then discover a reference to Mohammed therein. As it is, since Scripture says "I shall increase him bimeod meod," it can only denote an extravagant increment in numbers.
There is no question that the Divine assurance to Abraham to bless his descendants, to reveal the Torah to them, and to make them the Chosen People, refers only to the offspring of Isaac. ”