Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.004A.

Section : Water leftover after people have drunk from the pot.

According to the shari’ah, such water is considered pure regardless of whether the one who drank from the pot was a Muslim, an unbeliever, a person in post-sex impurity or a menstruating woman.

Although Allah says in the Qur’an, “Verily, the idol worshippers are impure” (at-Taubah) this is a reference not to their physical state, but to their false beliefs and creed. They may come into contact with dirt or impurities, but this does not mean that their possessions or bodies are impure. In fact, they used to mix with the Muslims. Their emissaries and delegations used to visit the Messenger of Allah and enter his mosque. The Prophet, upon whom be peace, did not order that the objects they touched be cleansed. As for menstruating women, ‘Aishah said, “I used to drink (from a container) while I was menstruating. I would then pass it to the Messenger of Allah and he would drink from the same spot where I had put my lips.” (Related by Muslim.)