QuestionIs it permissible for the fasting person to break a voluntary fast whenever he wishes? AnswerYes, it is permissible for him to do so. However, it is preferable for him to complete the fast unless there is a need to break the fast, such as honoring a guest, extreme heat or something similar to that. This is because of what has been confirmed from the Prophet (Sallallahu Alayhi wa Sallam) in the Hadith of Aishah (Radhi Allahu Anha) indicating what we have said.
And Allah is the Giver of Success.
Shaikh Ibn Baz (Rahimahullah)
Reference: Fatawa Islamiyah Volume 3 Pages 333-339