If someone were to ask: What do you say about a fasting person who intends to eat or drink forgetfully? Must someone else alert him?

Answer: He must, due to Allah’s saying:

“Cooperate with one another in righteousness and piety.” [al-Ma'idah 5:2]

Issue: A man has only one congregant praying behind him, and that congregant says subḥān Allāh to alert him. Should he go back to what the congregant says, or act upon what he himself believes?

Answer: He should not go back merely on the congregant’s statement. Yet sometimes, when the congregant alerts him, it gives him a preponderant likelihood that the congregant is correct. If he has such a preponderant likelihood, then—according to the stronger view—it is obligatory for a person to act upon it with regard to additions and omissions. Accordingly, he must go back in this case because of that. This often occurs when two latecomers arrive and join the prayer: sometimes one of them forgets and relies on the companion who arrived with him, so he prolongs his prostration in order to see whether the other will sit or stand. If he sees him sitting, he sits; and if he sees him standing, he stands.

An action customarily regarded as excessive, and which is not part of the prayer itself, invalidates it whether done deliberately or forgetfully, ..........

His statement: “An action customarily regarded as excessive.” “Action” is the subject, “regarded as excessive” is its adjective, and the clause “invalidates it” is the predicate of the subject.

His statement, “an action regarded as excessive,” means an action judged to be excessive. Had the author simply said, “excessive,” there would have been no need for the phrase “regarded as excessive,” since the meaning is the same.

“Customarily” means according to people’s customary usage. Thus, if people say, “This action is excessive in the prayer,” then it is customarily regarded as excessive. If they say, “This is a minor action,” then it is minor.