Bismillahi Al-Rahmani Al-Rahim
If one intends to keep a nafl fast and then breaks that fast, is it
Fardh or Wajib on that person to keep a fast? What is the ruling of
the Hanabilah on this issue?
Someone who begins a voluntary fast is permitted to break it. If one breaks a voluntary fast it is recommended to perform it at some other time, though it is not obligatory. The text from Zad al-Mustaqni` in the Book of Fasting includes:
It is unlawful to interrupt an obligatory action (b: whether it be fasting or something else) which has a vast time once it has been started.
It is not obligatory to complete a supererogatory action, or to make up one that is spoiled except for a supererogatory Hajj or `Umra. (section 4.3)
And Allah knows best.
Wa al-salamu `alaykum,