Rava argued that one may deduce from Isaac's example that a man may remain for 20 years with an infertile wife. For of Isaac, says, "And Isaac was 40 years old when he took Rebekah . . . to be his wife," and says, "And Isaac was 60 years old when she bore them" (which shows that Isaac waited 20 years). Rav Nachman replied that Isaac was infertile (and he knew that the couple was childless because of him). Rabbi Isaac deduced that Isaac was infertile from which says, "And Isaac entreated the Lord opposite his wife." Rabbi Isaac taught that does not say ""for" his wife" but ""opposite" his wife." Rabbi Isaac deduced from this that both were barren (as he had to pray for himself as well as her). The Gemara countered that if this were so, then should not read, "And the Lord let Himself be entreated "by him"," but rather should read, "And the Lord let Himself be entreated "by them"" (as Isaac's prayer was on behalf of them both). But the Gemara explained that reads, "And the Lord let Himself be entreated "by him"," because the prayer of a righteous person who is the child of a righteous person (Isaac son of Abraham) is even more effective than the prayer of a righteous person who is the child of a wicked person (Rebekah daughter of Bethuel). Rabbi Isaac taught that the Patriarchs and Matriarchs were infertile because God longs to hear the prayer of the righteous.