Rules of Oath.
2825. Oath has two types:
A. Oath for doing or avoiding to do a certain act in future.
B. Oath for proving or disproving something or issue.
2826. 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.
2827. If a person takes an oath, then if his word is correct, taking the oath is Makrooh; but if it is a lie, then he has committed a Haraam act and a great sin, but he has not to pay Kaffarah of oath. But, if a person takes a false oath to save himself to another Muslim from cruelty, there is no harm in it, and even sometimes it is obligatory. But, if he can perform Torieh, which means he takes oath in a way that it is not really the false one, then he should do that. For example, if a cruel person wants to harm somebody and he asks a person if he has seen a particular person and one has seen that person one hour ago and he says I have not seen him with the intention of referring to five minutes ago.
2828. The conditions for validity of an oath are:
I. A person who takes an oath should be Baligh and sane, and if he wishes to take oath on his property, he should not be feeble-minded or barred from right of discretion over his property by Shariah judge, and do it 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.
II. An oath taken for the performance of an act, which is Haraam or Makrooh, is not valid. Similarly, if he takes 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. Similarly, if he take an oath for renouncing a usually permissible act, it will be valid, if it is deemed more preferable than its performance, by the sensible people.
III. 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. In fact, if he uses other names or attributes of Allah, which do not remind of him, but give that connotation when used during an oath, even then the oath will be valid, as a precaution.
IV. 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.
V. 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. And the same rule applies if acting upon ones vow oath, or covenant involves Haraam or inappropriate acts.
2828. 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.
2829. If a son takes an oath without the permission of his father, or a wife takes an oath without the permission of her husband, may be it is correct but precaution is necessary.
2830. 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.