Берешит 17:9 Галаха: Mishneh Torah, Circumcision & Mishneh Torah, Kings and Wars

Mark how strictly the observance of Circumcision is to be regarded. Moses, although he was on a journey did not receive indulgence a single hour for neglecting this duty. In connection with all the precepts of the Torah, three covenants were made with Israel; as it is said "These are the words of the covenant which the Lord commanded … beside the covenant which He made with them in Horeb" (Deut. 28:69). And in the next section it is said "Ye are standing this day all of you before the Lord your God … that thou shouldst enter into the covenant of the Lord thy God" (Deut. 29:9-11). Three covenants are here mentioned. But in connection with Circumcision, thirteen covenants were made with our ancestor Abraham: "And I will make My covenant between Me and thee" (Gen. 17:2); "As for me. behold, My covenant is with thee" (ib. 17:4); "And I will establish My covenant between Me and thee" (ib. 17:7); "for an everlasting covenant" (ib. 17:7); "And as for thee, thou shalt keep My covenant" (ib. 17:9); "This is My covenant which you shall keep" (ib. 17:10) "And it shall be a token of a covenant" (ib. 17:11); "And My covenant shall be in your flesh" (ib. 17:13); "for an everlasting covenant" (ib. 17:13); "he hath broken my covenant" (ib. 17:14); "And I will establish My covenant with him" (ib. 17:19); "for an everlasting covenant" (ib. 17:19); "But My covenant I will establish with Isaac" (ib. 17:21).

Circumcision was only commanded of Abraham and his descendents, as it says, “You and your descendents who will follow you throughout the generations” (Genesis 17:9). Ishmael’s descendents are excluded from this Commandment, as it says, “For through Isaac shall your descendents be called yours” (Genesis 21:12). Esau is excluded since Isaac said to Jacob, “and he shall give the blessing of Abraham to you and to your descendents” (Genesis 28:4). Since he, alone, was the descendent of Abraham who stood fast with his religion and his upright ways, it is his progeny who were commanded with circumcision.