"And do not say of anything, 'I will do that tomorrow,' except (if) Allah wills." He says: Unless you make an exception (istithna').
Muhammad said: The meaning is: Unless you say: If Allah wills. Thus, the speech is implied; Abu Ubayd mentioned this.
His saying: "And remember your Lord when you have forgotten."
Yahya said: "It reached us that when the Jews asked the Messenger of Allah about the Companions of the Cave, the Messenger of Allah, peace be upon him, said to them: I will inform you of it tomorrow. He did not make an exception, so Allah revealed this verse."
Al-Hasan said: He was commanded not to say regarding anything in the future: 'I will do that tomorrow,' without making an exception: 'Except if Allah wills.' And he was commanded to make an exception if he remembers. Al-Hasan used to say: If a man swears an oath regarding something while he is mindful of the exception but does not make it, then there is no exception for him. But if he swears an oath regarding something while he is forgetful of the exception, then his exception holds as long as he remains in that gathering, whether he has spoken (after the oath) or has not spoken."
