What is the ruling on a person vowing to fast three days whenever they commit a specific sin? Is he obligated to fast them consecutively with an unannounced intention of consecution? Can expiation (fidyah) be offered in lieu of them? Can he go back on the vow after fulfilling what has accumulated upon him?

The scholars disliked repeated vows (nadhr (definition)) and the Messenger of Allah, peace and blessings be upon him, forbade it, saying: "Indeed, it does not avert anything; rather, it is used to extract from the miserly." This type of vow is called the vow of obstinacy (nadhr al-lajaj), and its maker has the choice between fulfilling what he committed to or offering an expiation for an oath (kaffarat yamin (definition)). There is no harm in quoting from the Qur'an for purposes that parallel the purposes of the Qur'an.