Halakhah for Sanhedrin 151:27

אמר אביי

Now, whence do we derive a formal prohibition of incest with an illegitimate daughter? This is in order according to Abaye and Raba: from the verse from which they deduce punishment, they also learn the prohibition.<span class="x" onmousemove="('comment',' Both being stated in the verses they employ for this purpose. ');">²⁶</span> But what of the deduction made by R. Abin's father?<span class="x" onmousemove="('comment',' Lev. XXI, 9 speaks only of punishment, but contains no prohibition. ');">²⁷</span> — R. Elai answered: The Writ sayeth, Do not profane thy daughter to cause her to be whore.<span class="x" onmousemove="('comment',' Lev. XIX, 29. This includes incest, and since 'daughter' in general is mentioned, it applies to an illegitimate one too. ');">²⁸</span> R. Jacob, the brother of R. Aha b. Jacob objected: Is this verse, Do not profane thy daughter to cause her to be a whore, employed for this purpose? But it is needed for that which has been taught: 'Do not profane thy daughter, to cause her to be a whore' I might think that this prohibits<span class="x" onmousemove="('comment',' Lit., 'the Writ speaks of a priest etc.' ');">²⁹</span> a priest from marrying his daughter to a Levite or an Israelite:<span class="x" onmousemove="('comment',' Since he thereby 'profanes her', in that she is not permitted to eat of terumah (v. Glos.) thereafter. ');">³⁰</span> therefore Scripture states, 'to cause her to be a whore', shewing that the reference is only to profanation by harlotry, thus prohibiting the giving over of one's daughter for sex purposes without marriage intention'? If so, Scripture should have said al tahel; why al tehallel? — That both may be deduced from it.<span class="x" onmousemove="('comment',' The latter [H] is a heavier form, yet with the same meaning [H], the former. Being heavier, it has a wider application. ');">³¹</span> Now, how do Abaye and Raba utilize the verse, Do not profane thy daughter to cause her to be a whore? — R. Mani said: [According to them] this refers to one who marries his [young] daughter to an old man.<span class="x" onmousemove="('comment',' Since she cannot willingly accept him, she may be led to adultery. ');">³²</span> As it has been taught: Do not profane thy daughter to &nbsp; &nbsp; cause her to be a whore; R. Eliezer said: This refers to marrying one's [young] daughter to an old man. R. Akiba said: This refers to the delay in marrying off a daughter who is already a bogereth.<span class="x" onmousemove="('comment',' Having attained puberty, she may become unchaste if not married. Marriage, of course, was then at a far earlier age than now. ');">³³</span> R. Kahana said on R. Akiba's authority: The only poor in Israel is the subtly wicked and he who delays in marrying off his daughter, a bogereth.<span class="x" onmousemove="('comment',' This is explained further on. ');">³⁴</span> But is not one who thus delays himself subtly wicked?<span class="x" onmousemove="('comment',' Why 'and he who delays etc.': the two are identical. His wickedness consists in that he keeps her unmarried, that he may profit by her labour whilst endangering her chastity. ');">³⁵</span> Abaye answered:

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