It is narrated from Sa’d ibn Abdullah, from Musa ibn Al-Hasan, from Ahmad ibn Hilal, from Muhammad ibn Abi Umayr, from Abdullah ibn Al-Mughirah, from a man: Abu Abdullah عليه السلام was asked regarding a woman who sees blood. Imam عليه السلام said: "If her menstrual period is less than ten days, she waits until the completion of ten days. If her period lasts ten days, she does not add any precautionary days."