Under what circumstances a patient is allowed to break fast?

Ibn Hajar al-Haythami in his book “Tuhfat al-Muhtaj” writes, “It is permissible for a sick person not to fast in the month of Ramadan or any other obligatory fast, if it can cause harm to the person so much that will make him resort to tayammum (in the presence of water).” [1]
“The third reason permitted for tayammum, is a condition in which there is a danger that the use of water can cause serious illness or aggravate it, but it is not mild headache or slight discomfort. It is also a danger of delaying recovery even in the absence of complications during the course of the illness.” [2]
“It is necessary to have an intention for Sharia permission (rukhsa) not to observe fasting because of illness.” “If a traveler and a sick person do not observe fasting, then they are obliged to reimburse it after the cause has been eliminated.” [3]
According to Imam Ibn Hajar, a sick person is not only allowed to break the fast, but also the nonobservance of fasting is imputed, if there is a risk of a health hazard, aggravating a current disease or delaying the healing process. It is necessary to distinguish a serious disease from a mild ailment.
Is fasting considered valid if a person eats during the morning azan?
Imam al-Ramli, in his book “Nihayat al-Muhtazh” writes, “If upon the occurrence of a precise dawn (i.e. the morning prayer time), a man has food in his mouth and he spat it out, then his fast is valid even if the involuntary penetration/ swallowing of food occurs.”
“... If a person does not spit it out immediately, but keeps the food in his mouth, then in this case the fast does not break. But if something will penetrate beyond his throat into the interior, even involuntarily, then his/her fast is broken, as if the person during the day put food in his mouth and it had inevitably penetrated inside.” [4]
References:
- Tuhfat al-Muhtaj, vol. 3, p. 429.
- Tuhfat al-Muhtaj, vol. 1, p. 343.
- Tuhfat al-Muhtaj, vol. 3, p. 431-432.
- Nihayat al-Muhtazh, vol.3, p.175.