Using dung ash in tooth powder

Question

Burnt dung, that is, ash, is mixed into tooth powder, which increases its effectiveness. May this ash be used?

Answer

Dung is impure; however, after burning, when it has become ash and its essence has changed, its ruling has changed as well: this ash will no longer be called impure. Therefore mixing it into tooth powder and using it will also be permissible.

Source: Fatawa Mahmudiyya

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