Reference for Yevamot 220:10
היכי דמי אילימא בפקחים ולבסוף נתחרשו מי מצי מפקי והתנן נשתטית לא יוציא נתחרש הוא או נשתטה לא יוציא עולמית
from [teachings] which he could parry by replying that the sisters [spoken of are such as were] originally deaf, and that the strangers [are such as were originally] of sound senses who became deaf afterwards? You should rather have raised your objection against him from the following: If two deaf brothers were married to two sisters who were of sound senses, or to two deaf sisters or to two sisters one of whom was of sound senses and the other deaf; and so also if two deaf sisters were married to two brothers who were of sound senses, or to two deaf brothers, or to two brothers one of whom was of sound senses and the other deaf, behold these women<span class="x" onmousemove="('comment',' If their husbands died without issue. ');"><sup>25</sup></span> are exempt from levirate marriage and from <i>halizah</i>.<span class="x" onmousemove="('comment',' Because all these marriages having been contracted by signs and gestures, are of equal validity. Each widow is, therefore, forbidden to the respective levir as his wife's sister. ');"><sup>26</sup></span> If [however the women] were strangers<span class="x" onmousemove="('comment',' To one another. ');"><sup>27</sup></span>