such things, one is not certain that they have come into contact with this particular water. Certainty is not displaced by doubt.

The second response:

The very same objection applies to street mud, given how frequently animal urine comes into contact with it. Yet Ahmad’s followers and others have held it to be ritually pure. Indeed, impurities in street mud are more abundant and persistent: even if an impurity mixes with some of the bathhouse water, it flows away rather than remaining, unlike what happens with street mud.

The third response:

Just as the original presumption is that no impurity is present, the apparent circumstances support that presumption. If we compare the water that ordinarily comes into contact with impurities with that which does not, the latter is far more abundant. Most of the water flowing over the bathhouse floor does not ordinarily come into contact with impurities. When the original presumption and the apparent circumstances agree, the matter is no longer a point of disagreement but one of consensus.

For this reason, I have said that washing it on the grounds that it is ritually impure is not recommended, for that is obsessive misgiving.

Within our school, there are two views on whether someone who doubts the ritual purity of water is advised to investigate whether it is impure. The stronger view is that such investigation is not recommended, because of the report concerning ‘Umar. This is because a ruling concerning an unperceived matter becomes binding only once it is known, according to the correct view, which is the apparent position of Ahmad’s school and the position of Mālik and others. Nor is anyone required to repeat the prayer if he did not know that he had on him