Reference for Keritot 34:33
חתיכה אחת ספק של חלב ספק של שומן ואכלה פטור
If it is doubtful whether [what is born] is a nine-months' child of the first husband or a seven-months' child of the second,<span class="x" onmousemove="('comment',' This refers to a woman whose husband had died childless and who married thereupon his brother, according to the law of levirate marriage, Deut. XXV, 5-10. Contrary to the law she married him before the prescribed three months had elapsed from the time of her husband's death, and after seven months she gave birth to a child. The paternity of the child raises doubts whether it was a premature birth and the child is of the second husband, or a normal birth and it is of the first. In the latter case she may not continue to live with her brother-in-law, for the law of levirate marriage would not apply and her past relations with him were incestuous.');"><sup>19</sup></span>