Ali ibn al-Hasan, from Ayyub ibn Nuh, from Muhammad ibn Abi Hamzah, from Ali ibn Yaqtin:
From Abu al-Hasan عليه السلام, regarding a man performing Wudu' (ablution) with the leftover water (su’r[4]) of a menstruating woman. Imam عليه السلام said: "If she is trustworthy, then there is no harm."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 1, p. 235
[4] Leftover water (su’r) – this is the water inside the vessel that remains as ‘leftover’ after having been used by a person, such as by dipping their hands into this vessel to draw water. In this example, the leftover water of a menstruating woman is not inherently impure. However, there is an implicit precaution: if there is a reason to believe the water may have been contaminated (for example, if her hands were impure when she dipped them into the vessel), then caution should be exercised
