Narrated by the Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, from Ahmad ibn Muhammad, from Muhammad ibn Yahya, from Muhammad ibn Ali ibn Mahbub, from al-Abbas, from Uthman ibn Isa, from Sama’ah, from Abu Abdullah عليه السلام, who said: I asked Imam عليه السلام about a woman who sees signs of purity but also observes a yellowish discharge or something similar and is unsure whether she has become pure or not. Imam عليه السلام said: "If this is the case, let her stand and press her abdomen against a wall, raising her leg onto the wall as you see a dog doing when it wants to urinate. Then she should insert a piece of cotton. If there is blood present, even as small as the tip of a fly, it will come out. If blood emerges, she has not become pure. If no blood emerges, then she has attained purity."