Sahih Muslim Book 8, Hadith Number 3413.

Chapter: It is forbidden to marry the step daughter and the sister of the wife (when the wife is alive and not divorced).

Umm Habiba, the wife of Allah’s Apostle (May peace be upon him), reported that she said to Allah’s Messenger (May peace be upon him): Messenger of Allah, marry my sister ‘Azza, whereupon Allah’s Messenger (May peace be upon him) said: Do you like it? She said: Yes, Messenger of Allah, I am not the exclusive wife of yours, and I wish that the person who joins me in good should be my sister. Thereupon Allah’s Messenger (May peace be upon him) said: That is not lawful for me. I said: Messenger of Allah, we discussed that You intend to marry Durrah bint Abu Salama. He (the Holy Prophet) said: You mean the daughter of Abu Salama? She said: Yes, whereupon Allah’s Messenger (May peace be upon him) said: Even if she were not the step-daughter of mine, brought up under my guardianship, she would not have been lawful for me, for she is the daughter of my foster-brother. Thuwaiba gave me suck and to Abu Salama (also), so do not offer to me your daughters and sisters.