Ruling 2688

An oath must fulfil the following conditions [for it to be valid (ṣaḥīḥ)]:

1. the person taking the oath must be of the age of legal responsibility (bāligh), and sane (ʿāqil). He must also have an intention (qaṣd) to take the oath and to take it of his own volition (ikhtiyār). Therefore, an oath taken by a child, an insane or intoxicated person, or someone who has been compelled, is not valid. The same applies [i.e. an oath is not valid] if it is taken by someone who in his anger took it unintentionally or did not take it of his own volition;

2. the act for which one takes an oath must not be unlawful (ḥarām) or disapproved (makrūh). And the act that one takes an oath to refrain from must not be an obligatory (wājib) or recommended (mustaḥabb) act. If a person takes an oath to do – or refrain from doing – something that is permissible (mubāḥ), in the event that doing it or refraining from doing it is something that would be preferred in the opinion of rational people or it is in the person’s worldly interest, the oath is valid;

3. a person must swear by one of the names of the Lord of the worlds that are reserved exclusively for His Holy Essence, such as ‘God’ and ‘Allah’. Alternatively, Allah the Exalted may be invoked using words that describe attributes and actions exclusive to Him; for example, one can say, ‘I swear by the one who created the heavens and the earth’. If one swears by a name that is also used for a being other than Allah the Exalted, but it is used so frequently to refer to Allah the Exalted that whenever someone mentions it, the Holy Essence of the Lord comes to mind – such as swearing by ‘the Creator’ (al-Khāliq) or ‘the Sustainer’ (al-Rāziq) – this too is valid. In fact, if one swears by a name that only comes to mind when one is taking an oath – such as ‘the All-Hearing’ (al-Samīʿ) and ‘the All-Seeing’ (al-Baṣīr) – then again the oath is valid; 

4. one must verbally say the oath. However, if a dumb person takes an oath by using sign language, it is valid. And if a person who is unable to speak writes it down and intends it in his heart, it is sufficient. In fact, if a person who is able to speak writes it down, then based on obligatory precaution (al‐iḥtiyāṭ al‐wājib) he must fulfil it;

5. it must be possible for one to fulfil the oath. If at the time of taking the oath it is not possible for one to fulfil it but afterwards it becomes possible, it is sufficient. If at the time of taking the oath it is possible for one to fulfil it but afterwards he becomes unable to fulfil it, then his oath becomes annulled from the time he became unable to fulfil it. The same applies if fulfilling the oath becomes so excessively difficult (mashaqqah) for him that he cannot endure what it takes to fulfil it. If him not being able to fulfil the oath was due to his own free actions, or it was not due to his own free actions but he did not have a legitimate excuse (ʿudhr) for delaying the fulfilment of the oath when he was able to fulfil it, then he will have sinned and kaffārah is obligatory for him.