Ante-Nicene Fathers, Vol VIII:
Two Epistles Concerning Virginity.: Chapter XI

Chapter XI.—Admonitory History of the Incestuous Children of David.

Hast thou not read concerning Amnon and Tamar, the children of David?  This Amnon conceived a passion for his sister, and humbled her, and did not spare her, because he longed for her with a shameful passion; and he proved wicked and profligate because of his constant intercourse with her, without the fear of God, and he “wrought uncleanness in Israel.” 483   Therefore, it is not proper for us, nor right for us, to associate with sisters, indulging in laughter and looseness; but we ought to behave towards them with all chasteness and purity, and in the fear of the Lord.

Footnotes

Gen. xxxiv. 7.