הַבָּא עַל יְבִמְתּוֹ, בֵּין בְּשׁוֹגֵג, בֵּין בְּמֵזִיד, בֵּין בְּאֹנֶס, בֵּין בְּרָצוֹן, אֲפִלּוּ הוּא שׁוֹגֵג וְהִיא מְזִידָה, הוּא מֵזִיד וְהִיא שׁוֹגֶגֶת, הוּא אָנוּס וְהִיא לֹא אֲנוּסָה, הִיא אֲנוּסָה וְהוּא לֹא אָנוּס, אֶחָד הַמְעָרֶה וְאֶחָד הַגּוֹמֵר, קָנָה, וְלֹא חָלַק בֵּין בִּיאָה לְבִיאָה:
Wer seiner Schwägerin beiwohnt, sei es aus Versehen oder aus Mutwillen, sei es gezwungen oder freiwillig, selbst wenn er aus Versehen und sie aus Mutwillen, er aus Mutwillen und sie aus Versehen, er gezwungen und sie nicht gezwungen, sie gezwungen und er nicht gezwungen handelt, gleichviel ob er sie dabei nur entblösst oder die Beiwohnung vollendet — erwirbt sie als Gattin; auch macht hierbei die Art der Beiwohnung keinen Unterschied.
Tosefta Ketubot
The [legal] power of a wife is greater than the power of a yevamah (one whose husband died with no children and now is in a legal bond with her former brother-in-law which either ends in marriage or halitzah) [in some respects], and the power of a yevamah is greater than the power of a wife [in other respects]. The power of a wife is stronger—for a wife eats terumah [if her husband is a kohen] as soon as she enters the bridal chamber, even before she has had sex—which is not true for the yevamah. The power of the yevamah is stronger—for a man who has sex with his yevamah (i.e. his dead brother's wife), whether intentionally or unintentionally, whether forced or willingly, even if she is in her father's house, he acquires [her as a wife]—which is not true of a wife [with whom a man would need to have sex with the purpose of betrothal].