Am I entitled to take a decisive oath that my husband has not paid school fees for three years, even though he paid for two of those years, so that I can collect other expenses for my children that he refused to pay and that are difficult to prove legally?

If a judge administers an oath to a person, and the judge is not unjust, then it is not permissible for the one taking the oath to lie or use dissimulation (tawriya). This is based on the Prophet Muhammad’s (peace be upon him) saying: "Your oath is according to what your companion believes you to be truthful about." And in another narration: "The oath is according to the intention of the one administering it." Scholars have unanimously agreed that in this case, the oath of the one being sworn is bound by what the judge intended, and dissimulation is of no benefit, because the oath was legislated to protect rights and to deter opponents. Therefore, if a decisive oath is requested of you, and you know that what the judge is asking of you is false, it is not permissible for you to swear a false oath. Instead, you must seek a legitimate means to claim your right.