Sahih Bukhari Volume 1, Book 6, Hadith Number 297

Narated By Um Salama : While I was laying with the Prophet under a single woolen sheet, I got the menses. I slipped away and put on the clothes for menses. He said, “Have you got “Nifas” (menses)?” I replied, “Yes.” He then called me and made me lie with him under the same sheet.