If he forgets that he is able to obtain it and performs dry ablution, he must repeat [the prayer]. If, by his dry ablution, he intends states of ritual impurity …

The evidence for this is the saying of Allah, Most High:

“If you cannot find water, then resort to clean earth.” [al-Ma'idah 5:6]

His statement, “If he forgets that he is able to obtain it and performs dry ablution, he must repeat [the prayer],” means that if he knew there was a well near him but forgot, and then, after praying, found the well, he must repeat the prayer.

If it is asked: How can he repeat the prayer when Allah, Most High, says:

“Our Lord, do not take us to task if we forget or make a mistake.” [al-Baqarah 2:286]

The answer is that this concerns fulfilling a condition, and a condition is not waived through forgetfulness. Moreover, he was somewhat negligent; had he reflected carefully and considered the matter thoroughly, he would have remembered.

It was also said that he need not repeat it (1), since he did not deliberately intend to contravene Allah’s command. At the time he prayed, the full extent of his ability led him to conclude that there was no water around him.

The more prudent course is to repeat it. When scholars say, “the more prudent course,” they do not mean that it is obligatory. Rather, they mean that refraining from it or doing it is an act of scrupulous piety, so that a person does not expose himself to punishment. Here they distinguish between a precautionary ruling and a definitive ruling. Shaykh al-Islam (2), may Allah have mercy on him, mentioned this.

His statement, “If, by his dry ablution, he intends states of ritual impurity,” means that this single dry ablution suffices for all such states, even if they are of different kinds. States of ritual impurity may be of one kind, such as when a person urinates several times: these are instances of impurity of one kind, namely urination.