Don't trust a Muslim who swears an oath by God

(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:o20.2).)

o18.1 An oath is only valid from a person (O: whether Muslim or non-Muslim) who:

(a) has reached puberty;

(b) is sane;

(c) makes the oath voluntarily;

(d) and intends an oath thereby.

o18.2 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)).

o18.3 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 reverance to the thing sworn by.)

o18.4 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.