Is expiation binding upon a fiancée who falsely swore an oath that she did not go out with men?

Whoever falls into sin must conceal it. The sister can use allusive speech (ma'arid) to make her fiancé understand that she does not go out with non-mahrams, without lying. If lying becomes necessary and she finds no other way, it is permissible for her, but without swearing an oath.

As for swearing a false oath intentionally, it is not permissible; this is the 'al-Yamin al-Ghamus' (the immersing oath), which is one of the major sins that immerse its perpetrator in sin and then in Hellfire.

The majority of scholars hold that there is no expiation (kaffarah) for it, but rather repentance is obligatory. However, Imam Al-Shafi'i and one narration from Imam Ahmad were of the view that expiation is obligatory, which is feeding ten poor people, or clothing them, or freeing a slave. If one is unable to do so, then fasting for three days. Combining repentance with expiation is safer and more cautious.