Charles Ellicott Commentary Genesis 17:26

"In the selfsame day was Abraham circumcised, and Ishmael his son." — Genesis 17:26 (ASV)

In the selfsame day. —Hebrew, In the bone of this day, and so in Genesis 17:23 . 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.