Joined: May 2008
I would like to know whether or not it is a sin to break a voluntary fast intentionally?
 - In al-Imam Nawawi's [d.676] explanation of al-Imam Muslim's [d.261h] collection of authentic hadeeth there is a chapter heading named:
- The Permissibility of Breaking a Voluntary Fast without an Excuse -
In this chapter he mentions the hadeeth of 'Aisha, may Allah be pleased with her:
Aisha, may Allah be pleased with her, mentions that, "One day the Messenger of Allah, sallallahu alayhi wa salaam, entered the house. [Once he entered], I said to him, some visitors left a gift for us, and I put some of it away for you. He, sallallahu 'alayi wa sallam said,'What is it?' I said, hais (a well known 'Arab dish: dates mixed with cheese and fat). So he, sallallahu alayhi wa sallam, said,' show it to me.' Then, he,sallallahu alayhi wa sallam said, I began the morning fasting,' then, he, sallallahu 'alayhi wa sallam, ate from it. [i.e. He, sallallahu 'alayhi wa sallam broke, his fast.]" [Muslim with an-Nawawi's explanation 8/2707]
al-Imam an-Nawawi[d.676h] said, "This hadeeth is a clear proof that it is permissible to break a voluntary fast. Just as it is a person's choice to begin his fast, it is his choice to finish it. This is the opinion of some of The Companions, [al-Imam] ash-Shafi'ee, [al-Imam] Ahmad, Ishaaq [ar-Raahaway] and others." [Muslim with an-Nawawi's explanation 8/2708]
 - An-Nisaa'ee [d.303h] also mentions in his collection of hadeeth, the Messenger of Allah, sallallahu 'alayhi wa sallam said, "A voluntary fast is like preparing to use some of your money for charity. If you want to give it, you can, and if you don't want to give it, you don't have to.." [Al-Albanee says, "This hadeeth is hasan (good)." An-Nisaa'ee 363/2322]
And Allah, the Most High, knows best.
and if so what should one do in this situation?
What situation? If you break your fast?