Is water in a container belonging to a non-Muslim considered ritually pure for purification?
Chapter on What Necessitates Ghusl
Al-Mughni
Book of Purification
Primary text
The Prophet (peace be upon him) performed ablution from a shared vessel belonging to a previously hostile person (a Jew who invited him to bread and rancid fat). This establishes the permissibility of using such water. The basis is that disbelief is an internal state and does not cause external ritual impurity, just as other internal matters do not, and the underlying state of things is purity.
Supporting text
A distinction can be derived between People of the Book who refrain from consuming unlawful items like carrion and swine and those who do consume them, similar to the jurisprudential ruling concerning their vessels and clothing.