Sahih Bukhari, Chapter: Menstrual Periods

Once one of the wives of the Prophet did Itikaf along with him and she was getting bleeding in between her periods. She used to see the blood (from her private parts) and she would perhaps put a dish under her for the blood. (The sub-narrator 'Ikrima added, 'Aisha once saw the liquid of safflower and said, "It looks like what so and so used to have.")