Answered by Shaykh Faraz Rabbani
My wife was performing a voluntary fast, while doing house work could not keep up as she was feeling really weak so she broke the fast. What does she do now?
Answer:
Walaikum assalam wa rahmatullah,
If one breaks a fast, with or without an excuse, it becomes necessary (wajib) to make it up later, even if it was a recommended fast. [Ibn Abidin/Haskafi, Radd al-Muhtar `ala al-Durr al-Mukhtar]
Wassalam.