Scholars are unanimously agreed that a traveler is permitted to refrain from fasting.
Allah says: “(Fasting) for a fixed number of days; but if any of you is ill, or on a journey, the prescribed number (should be made up) from days later.” [Sûrah al-Baqarah: 184]
Allah says: “...but if any one is ill, or on a journey, the prescribed period (should be made up) by days later.” [Sûrah al-Baqarah: 185]
The Sunnah is full of instances where the Prophet (peace be upon him) refrained from fasting while on a journey in Ramadan.
Jâbir relates [Sahîh al-Bukhârî (1946) and Sahîh Muslim (1115)]:
We were with the Prophet (peace be upon him) on a journey when he saw a crowd of people surrounding a man and providing him with shade. He said: “What is this?”
They said to him: “He is a fasting person.”
So the Prophet (peace be upon him) said: “It is not part of righteousness to fast while on a journey.”
In one narration of this hadîth in Sahîh Muslim, the Prophet (peace be upon him) said: “Take the concession that Allah has granted you.” [Sahîh Muslim (1115)]
Anas relates [Sahîh al-Bukhârî (2890) and Sahîh Muslim (1119)]:
We were on a journey. Some of us were fasting and others of us were not. The people who were not fasting were the ones to give water to the riding animals and erect the tents.
Therefore, the Prophet (peace be upon him) said: “Those who did not fast today took the blessings.”
Jâbir relates [Sahîh Muslim (1114)]:
We had gone forth with the Prophet (peace be upon him) to Mecca in the year of its conquest. The prophet (peace be upon him) fasted until he arrived at the valley of Kurâ` Ghamîm. Then he called for water, raised it up, and then broke his fast. He then received word that some of his Companions had completed their fasts, so he said: “They are the disobedient ones. They are the disobedient ones.”
These hadîth and numerous others like them indicate that a traveler is granted the concession to break his fast during the month of Ramadan.
The journey that permits a traveler to break his fast is the same as the journey that permits a traveler to shorten the length of his prayers. This is defined as any travel that can rightly be described as a journey.
The majority of scholars have quantified this as being a journey whose minimum total distance is that of 4 barîd, which in modern terms is roughly 82 kilometers.
Other scholars, including Ibn Taymiyah, hold the view that the definition of a journey cannot be quantified by any specific distance The matter is instead referred to custom. Whatever is customarily viewed as being a journey will take the legal rulings of a journey, including the permissibility of shortening the prayers, breaking the fast, and all the other concessions that are associated with travel. This opinion has also been related from some of the Pious Predecessors
Source: Islam Today