is invalid: namely, a condition that conflicts with what the Sacred Law prescribes.
His statement, “but the marriage is valid”: because there is nothing that conflicts with the contract. According to them, what conflicts with the contract in its very basis invalidates the contract; what conflicts with its implications invalidates the condition while leaving the contract valid; and what conflicts with the unrestricted contract may be either valid or invalid.
His statement, “If he stipulates that she be Muslim”: the pronoun refers to the wife; that is, he stipulates that she be Muslim.
His statement, “but she proves to be a woman from the People of the Scripture”: then he has the right to annul the marriage. Thus, this is a valid condition, though the author, may Allah have mercy on him, did not arrange the discussion as it ought to have been arranged.
It is understood from his words that if he did not stipulate that she be Muslim, and she then proves to be a woman from the People of the Scripture, he has no right to annul the marriage. For example, a man marries a woman believing her to be Muslim, but when he consummates the marriage, he finds that she is Christian or Jewish. He has no right to annul it, because he did not stipulate that she be Muslim.
However, note that a customary condition is like an expressly stated condition. If you are in a country whose people are Muslims, and at the time of marriage the man says, “I marry you my daughter so-and-so,” and you reply, “On condition that she is Muslim,” the guardian would say, “Do you accuse my daughters of being disbelievers?!” Thus, if she is from an environment whose people are Muslims, there is no need to stipulate that she be Muslim, because it is understood that she is Muslim. If she then proves to be non-Muslim, he has the right to annul the marriage, without any problem.
If she proves to be a disbeliever who is not from the People of the Scripture, the marriage is invalid from the outset—for example, if it becomes apparent that she does not pray. This may indeed occur. The marriage is invalid from its very basis, and no bridal due is owed by virtue of it, whether this becomes known before or after consummation. However, if it is discovered after consummation, she is given the bridal due because he had intercourse with her, and he may seek recourse against the one who deceived him.