This is another article in the chapter Justice from the classical manual on Sharia called Reliance of the Traveller. The articles are posted one by one in the order they are given in the book.
018.0 OATHS (YAMIN)
(A: An oath is a solemn statement to do or refrain from something, or that something is true, such that if things turn out otherwise, the swearer must make an expiation (def: 020.2).)
018.1 An oath is only valid from a person (0: whether Muslim or non-Muslim) who:
( a) has reached puberty;
(b) is sane;
(c) makes the oath voluntarily;
(d) and intends an oath thereby.
018.2 The oath of someone whose tongue runs away with him and who unthinkingly swears an oath, or someone who intends a particular oath but unintentionally swears something else, does not count and is an unintentional oath (A: which is mentioned in the Holy Koran (n: at 5:89)).
018.3 An oath is only validly effected if sworn by a name of Allah Most High, or an attribute of His entity (dhat).
(N: It is offensive to swear an oath by other than Allah if one merely intends it as an asseveration of one’s statement, though it is unlawful to do so if one intends reverence to the thing sworn by.)
018.4 There are some names of Allah Most High that are applied to no one but Him, such as Allah, the All-merciful, the All-vigilant, and Knower of the Unseen. An oath sworn by any of these is valid without restriction.
018.5 Other names of Allah may be conditionally applied to other than Him, such as Lord (Rabb) (n: rabb bayt meaning, for example, home owner), the All-compassionate (al-Rahim) (n: rahim al-qalb meaning softhearted), or the Omnipotent (al-Qadir) (n: qadir ‘alayhi meaning capable of it; the second term of each of these examples indicating that Allah is not meant). An oath sworn by such names is validly effected unless the swearer specifically intends something else.
018.6 Other of Allah’s names are applied to both Him and His creatures, such as the Living (al-Hayy), the Existent (al-Mawjud), or the Seeing (al-Basir). An oath sworn by such names is not validly effected unless the swearer specifically intends it as an oath.
018.7 An oath sworn by the attributes of Allah that are inapplicable to creatures, such as Allah’s glory, His exaltedness, His endless eternality, or the Koran, is validly effected without restriction.
018.8 An oath sworn by divine attributes that are sometimes used to allude to creatures, such as Allah’s knowledge, His power, or His right, is validly effected unless the swearer intends something else by them, such as meaning by knowledge the things known, by power the things under its sway, or by right (n: the) acts of worship (n: that are His right), in which cases an oath has not been validly effected.
018.9 An oath is validly effected when a person says, “I swear by Allah that … ,” or “I’ve sworn by Allah that. .. ,” unless the person merely intends to inform.
018.10 Unless one particularly intends it as an oath, an oath is not validly effected when the following expressions are used: “I will not do such and such, by the life of Allah,” or “I resolve by Allah,” or “by the covenant of Allah,” “His guarantee,” “His trust,” “His sufficiency,” or “I ask you by Allah,” or “I swear by Allah that you must do such and such.”