An example of this is water in which the hand of a person who has risen from sleep at night that invalidates ablution has been immersed: it is pure but not purifying. If such water is confused with purifying water, he should neither investigate which is which nor perform dry ablution, because using the pure water here causes no harm. This differs from the previous case, in which purifying water was confused with impure water: if he were to use it, his garment and body would become impure.

Accordingly, he performs a single ablution, taking one scoop from this vessel and one scoop from that, because once he completes his ablution, he can be certain that he has performed ablution with purifying water, and his ablution is therefore valid.

If it is asked: Why does he not perform a complete ablution from this vessel, and then another complete ablution from the other?

The answer is that this is invalid for two reasons:

First: if he were to do so, he would finish each ablution while uncertain about it, and an intention tainted by indecision is invalid.

Second: if he performs a complete ablution from the first vessel—supposing that it is the purifying water—and then performs a complete ablution from the second, which is the pure water, he may become certain during the first ablution, or consider it more likely, that he used the purifying water in washing his hands and the pure water in washing his face; and during the second ablution, that he used the pure water in washing his hands and the purifying water in washing his face. Thus, the washing of the face by which ritual purity was attained would come after the washing of the hands, which is a failure to observe the proper sequence.

It should not be said that certainty is attained by combining the two, because when he performed either one, he was uncertain about it and not certain. He then offers one prayer.

Some scholars said: He performs ablution first, then prays, then performs ablution a second time.