Reference for Yevamot 200:11
ובזנות מי גזור רבנן והתנן מי שלא שהתה אחר בעלה שלשה חדשים ונשאת וילדה
HE RECEIVES A SINGLE PORTION.<span class="x" onmousemove="('comment',' Since one of the two is certainly his father. ');"><sup>31</sup></span> <b><i>GEMARA</i></b>. Only the <i>halizah</i> [must take place first]<span class="x" onmousemove="('comment',' Where HE HAD BROTHERS IN THE FIRST AND … SECOND, BUT NOT BY THE SAME MOTHER … ONE SUBMITS TO HALIZAH AND THE OTHER MAY [THEN] CONTRACT LEVIRATE MARRIAGE. ');"><sup>32</sup></span> and the levirate marriage afterwards; the levirate marriage, however, must not take place first, since, thereby, one<span class="x" onmousemove="('comment',' Should that brother not he the son of the father of the deceased. ');"><sup>33</sup></span> might infringe the prohibition against the marriage of a sister-in-law with a stranger.<span class="x" onmousemove="('comment',' Lit., 'for he met a sister-in-law for the market'. ');"><sup>34</sup></span>