From him, from Hammad, from Shu'ayb, from Abu Basir, from Abu Abdullah عليه السلام:
I asked Imam عليه السلام about a pregnant woman who sees blood. Imam عليه السلام said: "Yes, a woman may sometimes discharge blood while she is pregnant."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 1, p. 410