from an animal whose meat is not lawful to eat, there are two scholarly views on the matter, both represented within Ahmad’s school:

The first is that it is deemed impure, because the default ruling concerning dung is impurity.

The second—and more correct—view is that it is deemed pure, because the default ruling concerning substances is purity. The claim that the default ruling concerning dung is impurity is disputed: neither a scriptural text nor scholarly consensus establishes this. Anyone who asserts a default ruling without a scriptural text or consensus makes an unfounded claim. If his only basis is analogy, the dung of animals whose meat is lawful to eat is pure; how, then, can it be claimed that impurity is the default ruling concerning dung?

Once this is understood, if one is certain that the fuel is impure, its smoke falls under the question of transformation, as discussed above. If, however, one is certain that the fuel is pure, there is no disagreement concerning it. If one doubts whether it contains anything impure, the default ruling is purity. Even if one is certain that it contains dung but doubts whether that dung is impure, the correct ruling is that it is pure.

If one knows that the fuel contains both pure and impure matter, and we adopt the view that material resulting from the transformation of impure matter remains impure, then the resulting material has the same ruling as its source. Whatever reaches the bather’s body may come from the pure matter or from the impure matter, so the body does not become impure through doubt. Likewise, if some ash from fuel of this kind touches him, we do not deem his body impure on that account, even if we are certain that the fuel contains something impure. This is because that particular ash may not be impure, while the body is certainly pure; we therefore do not deem it impure on the basis of doubt. This applies when the impure ash has not mixed with the pure ash, or the impure vapour with the pure vapour.