Is it obligatory to fast for three consecutive days as expiation for an oath, after watching a single pornographic video, knowing that I vowed not to watch any pornographic films or videos?

A person should not make vows (nadhr), even if the intention is to encourage oneself to obey Allah or to abandon sin, for making vows is disliked (makrooh). Watching pornography and engaging in sexual relations outside of marriage are forbidden. Whoever vows not to commit a sin and then commits it, must first repent, and then offer expiation for breaking an oath (kaffarat yameen), which is: feeding ten poor persons, or clothing them, or freeing a slave. If unable to do any of these, then one must fast for three days.