I was with a person during Ramadan in a city other than my city of residence. We heard the sunset call to prayer on the radio and broke our fast, thinking it was the local call to prayer. Shortly afterward, a nearby mosque made the actual call to prayer, and we realized that we had broken our fast before the proper time. What is the ruling on our fast for that day?

Fasting means the abstention from things that break the fast from the break of dawn until sunset. Islamic Law requires that the fasting person exercise caution in observing the fast and not to break it except after ascertaining that the sun has indeed set. Allah Almighty says, “Then complete the fast until the night” (Quran, 2:187), meaning that the first part of the sun's disk has definitely set.

Islamic jurists have determined that if a fasting person exercises judgment and believes that the sun has set, then eats and later finds out that he was mistaken, his fast is invalid because the error in his judgment has become clear. An assumption that is clearly proven wrong is of no consequence in Islamic law. ‘Umar ibn al-Khattab (may Allah be pleased with him) once broke his fast in Ramadan on a cloudy day, thinking that it was evening and that the sun had set. A man came to him and said, “O Commander of the Faithful, the sun came out.” ‘Umar said, ‘The matter is simple; we exercised our best judgment’” (recorded by al-Bayhaqi in his Sunan). Imam al-Shafi‘i commented, “This means that he instructed that a day be made up in its place.”

Based on the above, although the inquirer is not sinful for breaking his fast before sunset, he must nevertheless make up that day, and the same applies to the person who broke the fast with him.

And Allah Almighty knows best.