Tractate Yevamot - Chapter 14 - Mishnah 5

If two brothers of sound senses were married to two sisters one of whom was deaf and the other of sound senses, and the brother of sound senses, the husband of the deaf sister, died, what should the brother of sound senses, the husband of the sister who was of sound senses, do? [Nothing, since she is] exempt because she is his wife’s sister. If the brother of sound senses, the husband of the sister who was of sound senses, died, what should the brother of sound senses, the husband of the deaf sister, do? He must release his wife with a get and his brother’s wife by halitzah.