Reference for Yevamot 64:4
וכ"ת מגו דאיתסר בכולהו אחוותא האי איסור כולל הוא
And were you to reply: Because thereby<span class="x" onmousemove="('comment',' By marrying the other sister. ');"><sup>8</sup></span> he is forbidden to marry all the sisters,<span class="x" onmousemove="('comment',' While before this marriage the widow only was forbidden. ');"><sup>9</sup></span> [it may be retorted that] such is only a comprehensive prohibition!<span class="x" onmousemove="('comment',' [H] lit., 'a prohibition which includes'. The additional prohibition includes the widow in the same manner only as it does the other sisters but, unlike an issur mosif (the prohibition of the wider range, v. supra p. 202, n. 9), it does not place any additional restriction as far as the widow herself is concerned upon any other men. ');"><sup>10</sup></span>