Genesis 20:12

My sister, or niece, according to those who say she was daughter of Aran, who thus must have had a different mother from Abraham; (Menochius) or, as we rather think, Sara was truly his half-sister, born of Thare by another wife. His adding truly, seems to restrain it to this sense; and we know that in those countries, marriages of such near relations were allowed, though not when both had the same parents. Why should we not, therefore, believe Abraham, who certainly knew the real state of the question, and who would not tell a lie, rather than seek for improbable and far-fetched solutions? Said, who lived eight hundred years ago, mentions the name of Jona, Abraham's mother, as well as that of Tehevita, who bore Sara to Thare. The Hebrews, in general, give this explanation. (Calmet) --- By calling Sara his sister without any addition, Abraham intended that the people should conclude he was not married; therefore he did not say she was his half-sister, as this would have frustrated his design, if, as Clement of Alexandria, asserts, such might and did marry under the law of nature. (Haydock) --- Philo observes, the Athenian legislator, Solon, sanctioned the same practice, which was followed also by the Ph\'9cnicians. (Calmet)