purification in Islam
1-Leftover water from a human being:
It is reported “that the Prophet ﷺ used to drink from what A’ishah (may Allah be pleased with her) had drunk while she was menstruating, and he used to put his mouth on the place where she drank from.”[ narrated by Muslim.]
2-Leftover water from a cat:
The Prophet ﷺ said of the cat that drank from a container: “It (the cat) is not impure. It is merely one of your companions who frequently wanders amongst you.” [ narrated by At-Tirmidhi.]
3-Leftover water from animals whose consumption is permissible, as well as mules, donkeys, carnivores, hunting birds and their likes.
It is pure. This is because the basis of all things is purity when there is no evidence proving otherwise. It is well known that the Prophet ﷺ used to ride donkeys as did others during his time. This proves that donkeys are not impure.