[Using figurative and indirect expressions in oaths in the presence of those who do not understand them]

Answer: There is no objection to using figurative expressions and metaphors frequently in speech, except in certain situations, including:
 When the listener would be harmed because of what he heard.
 When the speaker would incur suspicion concerning his honor or his religion, and likewise any other person.
If the figurative expression or metaphor is free of such things and what resembles them, then there is no objection to using it.
And whoever swears, “This is my garment,” while intending “one like it,” is truthful in his oath. The scholars have said: An oath is according to the intention of the one who swears it, so long as the wording can bear that intention in its literal sense, or in an indirect (kināyah) sense, or a figurative sense – except in matters of legal rights, where it is according to the intention of the one who administers the oath.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2