1186 – Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (peace and blessings be upon him) said, “Your oath is to be understood according to what your companion deems you to mean.”
Another wording states, “An oath is judged by the intention of the one who demands it.” Both narrations are related by Muslim. (1)

What is derived from the ḥadith
1 – In legal disputes, the form of the oath corresponds either to the claimant’s allegation or to the defendant’s reply. Thus, if the judge—at the claimant’s request—has the defendant swear, he dismisses him once the oath is taken and the litigation ends, because an oath ends the dispute. If the oath is directed at the claimant and he swears, he thereby obtains what he claimed.

2 – The ḥadith shows that in lawsuits the oath required of a litigant must rest on the intention of the one who demands the oath; the swearer’s private intention is of no value if it differs from what he has outwardly declared. This is the consensus of the scholars. In the commentary on al-Iqnāʿ it is stated: “The litigant’s oath must be phrased in keeping with his answer to his opponent and he must not append to it anything unintelligible. Resorting to double meanings or strained reinterpretations is prohibited.”

3 – Accordingly, when a judge administers an oath to the party on whom it falls, the oath is governed by the judge’s intention, not by the hidden intention of the swearer. If the latter swears while intending something other than what he makes explicit, neither reinterpretation nor equivocation will avail him.

4 – Al-Nawawī said: “If a person swears without being instructed by a judge and employs an intentional ambiguity (tawriyah), the ambiguity is effective and he does not incur sin—whether he swore on his own initiative or at the request of someone other than the judge or his deputy. In such cases, the intention of the non-judicial requester carries no legal weight.”