From the sources
The Circumcision Ceremony According to the Talmud
Song of Ascents
The Treasury of Chassidim
Ecclesiastes Rabbah 5
Then the word of the Lord came to him: “This man will not be your heir, but a son who is your own flesh and blood will be your heir.” He took him outside and said, “Look up at the sky and count the stars—if indeed you can count them.” Then he said to him, “So shall your offspring be.” Abram believed the Lord, and he credited it to him as righteousness.
He also said to him, “I am the Lord, who brought you out of Ur of the Chaldeans to give you this land to take possession of it.”