From Sahih Bukhari (Hadith 309):
Narrated `Aisha:Once one of the wives of the Prophet (ﷺ) did I`tikaf 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)
Reference: Bukhari 309