It is narrated from Al-Ala ibn Razin, from Muhammad ibn Muslim, from Abu Abdullah عليه السلام, who said:
Imam عليه السلام said: "If the blood does not stop, the woman in a state of nifas (postnatal bleeding) refrains from prayer for thirty, forty, or up to fifty days."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 1, p. 186