In the seventh aliyah G-d makes a covenant with Avrohom and his descendants after him: that all males should be circumcised on the eighth day after birth. Sarai's name becomes Sarah in this aliyah.
Avrohom is circumcised, and also, all the males of his household. Avrohom is 99 years when his bris takes place, and Yishmael is 13 years old when his bris takes place.
