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Transformation (Istihala)

196. If a najis thing undergoes such a change, that it assumes the category of a Pak thing it becomes Pak; for example, if a najis wood burns and is reduced to ashes, or a dog falls in a salt-marsh and transforms into salt, it becomes Pak. But a thing do es not become Pak if its essence or category does not change; like, if wheat is ground into flour, or is used for baking bread, it does not become Pak.

197.
 Any earthenware which is made of najis clay, is najis. But coal derived from najis wood will be Pak, if it has no semblance of its origin.

198.
 A najis thing about which it is not known whether it has undergone any transformation (Istihala) or not, remains najis.