Is it permissible to observe expiatory fasting (siyam al-kaffarah) when swearing to do something in the future, then realizing a potential inability to do it, or must one wait until the breaking of the oath (al-hinth) actually occurs?

Scholars have differed regarding offering expiation before breaking an oath, with the majority permitting it. They based their view on what was narrated from Umar, Ibn Abbas, Salman, and others, and on the saying of the Prophet, peace and blessings be upon him: "If you take an oath, and then see something else better than it, then offer expiation for your oath, and then do that which is better." Therefore, it is permissible to offer expiation before breaking the oath, knowing that fasting is not sufficient except when one is unable to feed, clothe, or free a slave.