As if He said, Think not that if you perish the Patriarch will be deprived of sons, for God even from stones can produce men unto him, and prolong the line of his descendants. For so has it been from the beginning, seeing that for men to be made from stones unto Abraham is but equivalent to the coming forth of a son from the dead womb of Sarah.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: ubi sup.