Genesis 18:11

Now Abraham and Sarah [were] old, [and] well stricken in
age
The one being ninety nine years of age, and the other eighty nine; and which is observed to make it the more surprising that they should have a son at such an age; and what follows still makes it more so: [and] it ceased to be with Sarah after the manner of women;
her monthly visitors had left her, so that she was unfit for conception, and there could be no hope of it in a natural way; though the philosopher ^F23 intimates, that there are some, that it is possible, may conceive without them.