Must one verbally express the exception (Istithna) when swearing an oath?
General Chapter
Al-Mughni
Book of Oaths
Primary text
The exception must be uttered by the tongue; exception made only in the heart is ineffective. This is the position held by the general body of scholars, including Al-Hasan, Al-Nakha'i, Malik, Al-Thawri, Al-Awza'i, Al-Layth, Al-Shafi'i, Ishaq, Abu Thawr, Abu Hanifa, and Ibn Al-Mundhir. We know of no dissenters to this view. The evidence is the statement of the Prophet, peace be upon him: "Whoever swears, then says, 'If Allah wills' [In sha Allah]." Utterance constitutes the saying, and since the oath itself is not established by mere intention, neither is the exception.
Supporting text
It is narrated from Ahmad that if the person is oppressed and makes the exception internally while fearing for himself, it is hoped that it will be valid, because his oath is not established, or he is considered as one making a metaphorical interpretation (ta'wil). However, this concession applies only to one fearing for himself, not to others.