Clement of Rome

And again [the Scripture] says, "God brought forth Abram, and spoke unto him, Look up now to heaven, and count the stars if you are able to number them; so shall your seed be. And Abram believed God, and it was counted to him for righteousness." On account of his faith and hospitality, a son was given him in his old age; and in the exercise of obedience, he offered him as a sacrifice to God on one of the mountains which He showed him.