Muhammad ibn Ya'qub, from Muhammad ibn Yahya, from Salama ibn al-Khattab, from Ali ibn al-Hasan al-Tatari, from Muhammad ibn Abi Hamza, from Ibn Miskan, from Shurahbil al-Kindi, from Abu Abdillah عليه السلام, who said: Imam عليه السلام was asked: "How does a menstruating woman recognize her purity?" Imam عليه السلام replied: "She leans her left foot against the wall and inserts a piece of cotton with her right hand. If there is something like the tip of a fly (of blood) on the cotton, it indicates her condition."