Midrash for Yevamot 26:12

כיון דלא אתי איסור אשת אח וחייל אאיסור אחות אשה הויא לה צרת ערוה שלא במקום מצוה ושריא:

And the others? — They derive it from the use of ha-huzah where huzah could have been used.<span class="x" onmousemove="('comment',' The addition of the 'he' in [H] where [H] would have conveyed the same meaning implies the inclusion of the betrothed. (V. n. 6.) ');">³⁴</span> And the others? — A deduction from huzah ha-huzah does not appeal to them. Raba said: Beth Shammai's reason<span class="x" onmousemove="('comment',' V. p. 68, n. 2, supra. ');">³⁵</span>

Sifrei Devarim