Rules regarding oath (Qasam)
2679. If a person takes an oath that he will perform an act (e.g. that he will fast) or will refrain from doing an act (e.g. that he will not smoke), but does not intentionally act according to his oath, he should give Kaffarah for it, which means he should set a slave free, or should fully feed ten indigent persons, or should provide them with clothes. And if he is not able to perform these acts, he should fast for three consecutive days.
2680. The conditions for validity of an oath are:
1. A person who takes an oath should be Baligh and sane, and should do so with free will and clear intention. Hence, an oath by a minor, an insane person, an intoxicated person, or by a person who has been coerced to take an oath, will not be in order. Similarly, if he takes an oath involuntarily, or unintentionally, in a state of excitement, the oath will be void.
2. An oath taken for the performance of an act which is haraam or makrooh, is not valid. Similarly, an oath for renouncing an act which is obligatory or Mustahab is also void. And if he takes an oath to perform a normal or usual act, it will be valid, if that act has any preference in the estimation of sensible people.
3. The oath must be sworn by one of those names of the Almighty Allah which are exclusively used for Him, (e.g. 'Allah'). And even if he swears by a name which is used for other beings also, but is used so extensively for Him, that when any person utters that name one is reminded of Him Alone, for example, if he swears by the name Khaliq (the Creator) and Raziq (the Bestower), the oath will be in order.
4. The oath should be uttered in words, but a dumb person can take an oath by making a sign. Similarly, if a person is unable to utter the words, he may write down the oath, repeating in his mind the intention for it, that will be a valid oath, though as a precaution, he may confirm the oath in other ways as well.
5. It should be possible for him to act upon his oath. And if he was able to act upon the oath when he took it, but became incapable of acting upon it later, the oath becomes nullified from the time he became incapable of acting upon it, provided that he did not incapacitate himself purposely. And the same rule applies if acting upon one's vow, oath, or covenant, involves unbearable hardship.
2681. If the father forbids his son to take an oath, or the husband forbids his wife to take an oath, their oath is not valid.
2682. If a son takes an oath without the permission of his father, or a wife takes an oath without the permission of her husband, the father or the husband can nullify the oath.
2683. If a person does not act upon his oath because of forgetfulness, helplessness or heedlessness, he is not liable for Kaffarah. And the same rule applies, if he is forced not to act upon his oath. And if an obsessed person takes an oath like, if he says: "By Allah, I am going to offer prayers now at once," and then does not offer prayers owing to the whims haunting him, which renders him incapable of acting according to the oath it is not necessary for him to give Kaffarah.