Valid Excuses For Not Fasting

(the five major categories in brief)

Valid excuses for not fulfilling the obligations for fasting fall under five major categories (aside from menstrual and postnatal bleeding). When one breaks one's fast with a valid excuse, he should simply make up the missed day, whereas breaking the fast without a valid excuse entails a penalty, such as fasting consecutively for two months if one is able. Here is an expanded explanation of the five major categories of valid exemption from fasting.
1. The First Category: Illness
Illness is that which takes a person outside the bounds of health as the result of some indisposition. Ibn Qudaamah  says: "There is consensus among the scholars of the permissibility of breaking the fast due to illness in general, as evinced in the verse of the Quran: {...Yet if one among you is sick or is on a journey [such a person shall then fast] the same number of other days...} [Quran 2:185]
Salaam ibn Al-Akwa, may Allah be pleased with him, reported: "When the verse `wa alal-ladheena yooteeqoonahoo...' was revealed, whoever wanted to break their fast was allowed to break their fast and pay the ransom, until the verse ‘Shahru Ramadanal-ladhee...' was revealed and abrogated the one before it."
So, the prescription of fasting went through stages. First, it was permissible to break one's fast. Then it became necessary to fast unless one had an excuse for not doing so.
Illness was considered a valid excuse. It is not any illness or pain that allows one to break the fast. If someone is afraid that fasting will make the sickness worse or delay the cure, or cause damage to anything in the body, then he has a valid excuse to break his fast. In fact, he should break his fast. This is because it is an obligation for people to keep themselves from perishing.
As for a person who is well, it is not a sufficient excuse to break his fast if he feels fasting is difficult. The exception here, however, is the Hanafi opinion. According to the Hanafis, if a person who is well thinks it is very likely that he will become sick because of the fast, he can break his fast. But if this fear is not very real and more imaginary or just mental apprehension, then it is not permissible to break one's fast.
The Maalikis say that if the healthy person has no illness to begin with but he fears that fasting will cause an illness, then he cannot break his fast because there is no real proof—or that his fear is not sufficient proof.
However, if someone knows with great certainty that fasting will cause them real harm, they can break their fast. Real harm, here, is not to be confused with difficulty, as difficulty in fasting is a totally invalid excuse to break one's fast.
Yet the fact that a person who is ill should break his fast does not mean that if he chooses to complete his fast that it is invalid.
Some scholars divide the sick, in terms of the obligation of fasting, into four types:
a. One not able to fast or legitimately afraid of illness or excessive weakness if he fasts. In this case, the person must break his fast. It is an obligation to do so.
b. One who is able to fast but fasting imposes upon that person great hardship
c. One who is able to fast, but with great hardship, and afraid that fasting will make his sickness worse. Some say this person must, some say this person should, break the fast.
d. One who is fasting and for whom fasting does not present with any real danger, only real difficulty. In this case, one must fast.

II. The Second Category: Travel
The kind of travel that allows one to break one's fast must fulfill all of the following five conditions:
A. Long enough for one to shorten their prayers (about 50 miles according to most scholars, but what is considered by people a journey)
B. The person in the state of travel or far from home does not have the intention of staying at that destination for more than three days. In this latter case, the person may be permitted to not fast (during the travel if they fulfill the other three requirements), but must resume the fast when they arrive at their destination of more than three days.
C. According to the majority of scholars, the person undertaking the journey must not be making it for unlawful reasons or to unlawful destinations, like a gambling trip to Las Vegas. This is because the allowance to break one's fast is to make travel easy. If someone is undertaking an unlawful action, they are not included in the principle of creating ease for the traveler.
D. The Hanafis allow for someone who is traveling for something unlawful to break their fast because there is no text that specifies that the excuse is only for someone who is traveling for something lawful – and because the act of traveling itself is not unlawful. So, the exemptions, according to the Hanafis, is connected to traveling itself, not what comes after.
E. One must go beyond the limits of the city or town one is staying in. This means if one were to travel 50 miles but still be within his city or town area, it would not count as travel. The question of whether one's metropolitan area remains as one's town should be considered seriously, such as greater Chicago, for instance.
The majority of the Companions of the Prophet  were of the opinion that whoever starts Ramadan while settled and then travels after they started Ramadan, he is still allowed to break his fast because of the generality of the texts and because the Prophet  departed for the conquest of Makkah during Ramadan and broke his fast, even though he started his travel after Ramadan had started. This hadeeth was reported by Al-Bukhari.
In terms of the time of the permissibility of breaking fast, there are four situations, the last of which includes, not the traveling woman, but the breastfeeding or pregnant woman:
1. That he begin travel before Fajr (dawn) and he intend to break his fast. There is consensus here about his permissibility to break his fast because he was in a state of travel when the reason for the obligation of fasting commenced.
2. That he begin travel after the commencement of Fajr (dawn) and in this situation —according to the majority it is not permissible for him to break his fast since he began an obligatory fast in a state of being settled. However Ahmad ibn Hanbal  was of the opinion that once one commences travel, they are allowed to break their fast.
This opinion of Ahmad ibn Hanbal  is the accurate one due to the hadeeth reported by Muslim that the Prophet  headed for Makkah in the year of the conquest (of Makkah) in the month of Ramadan, and he traveled while fasting until he reached a certain place called Kiraa'Al-Ghameem. The people were fasting with him, and then it was said to him: "The fasting, indeed, has become a hardship for the people, and they are looking to see what you do." So the Prophet  called for a vessel of water after `Asr (afternoon) and drank in front of the people and some of them broke their fast while others continued.
When the news reached the Prophet, sallallaahu alayhe wa sallam, that some of them continued their fast, he commented: "Those are the disobedient ones."
Imaam Ahmad  reported, on the authority of Ibn `Abbaas, that the Prophet, sallallaahu alayhe wa sallam, left for Makkah in the Year of the Conquest, during the month of Ramadan and fasted until he reached a certain point on the road. This was around midday. At that point, he reached a water source, and he saw the people with him looking longingly at the water. So the Prophet  asked for a vessel of water, and he waited until all the people were looking at him, and he drank. So the people drank after him.
The scholars that say it is all right to break your fast after the commencement of the fast use this story as a proof for their opinion. They claim also as proof that the status of the traveler has precedence over the status of the settled person.
Most of the scholars, including the Hanbalis, hold that someone who intends to fast a day in Ramadan and then embarks on a journey, once he has begun that journey, should preferably not break his fast.
3. The majority of scholars say that breaking one's fast immediately before embarking on a journey—for example, breaking fast in one's home before leaving on a trip—is impermissible because the circumstance that allows for the permissibility of breaking one's fast is the traveling journey itself. So, one would have to wait until one is in a state of travel before breaking one's fast.
4. The jurists are in agreement that a breastfeeding or pregnant woman is allowed to break her fast, under the condition that she believes that fasting will cause harm to her or her baby. The Hanbalis actually hold the position that it is makrooh (disliked) for her to fast in this state. The proof for this is the hadeeth that At-Tirmithi reported that, "Indeed Allah, Transcendent and Resplendent, has relieved the traveler of the obligation of fasting and relieved him of half the prayer and likewise relieved the pregnant and breastfeeding woman of fasting."
III. The Third Category: Old Age
There is consensus that it is permissible for people who are elderly not to fast. There is no specific definition for old age. It pertains to what people know and agree to be an age that is very advanced and disabling.
IV. The Fourth Category: Thirst and Hunger
Severe thirst or hunger are valid excuses not to fast but not any kind of severe thirst or hunger. If someone really believes that the continuation of their fast will physically harm them because they are suffering from severe thirst and hunger, then it is permissible for them to break their fast. Also, if one is anticipating battle, that he will be engaged in battle, and he breaks his fast because of that anticipation, but the battle does not ensue, there is no penalty for having broken his fast.
V. The Last Category: Coercion
If someone were to threaten someone else with a real threat such as, "If you do not break your fast, you will be executed or jailed!" there is no penalty if one breaks his fast under such circumstance, but one is obliged to make up this missed fast.