Ellicott's Commentary for English Readers - Genesis 17:26
(26) In the selfsame day.—Heb., In the bone of this day, and so in Genesis 17:23 (see Genesis 2:23). In the circumcising of the household together with Abraham and his son we see that no impassable interval separated the Hebrew slave from his master, but that he was to share all the national and religious privileges of the freeman. read more
Ellicott's Commentary for English Readers - Genesis 17:25
(25) Ishmael. . . . was thirteen years old.—Hence the Mohammedans defer circumcision to the thirteenth year. read more