בראשית יח:יא פירוש: רש״י, רמב״ן, רד״ק וטור הארוך

חדל להיות means [that] it had ceased from her.

‘BA’IM BAYAMIM’ (ADVANCED IN DAYS). In his youthful days a man is called “standing in days,” and they are referred to as “his days” because they belong to him, just as in verse The number of thy days will I fulfill.⁹⁷Exodus 23:26. But when he gets old and has lived longer than most people of his generation, it is said of him that he is ba bayamim, [literally, “came into days”], because it is as if he came into another land, travelling from and arriving in a city each and every day.

ואברהם, this line has been written only in order to account for the reason of Sarah’s laughter.