When the month of Ramadan begins, every Muslim who is accountable, not travelling and in good health is obliged to fast. Allah says (interpretation of the meaning):
So whoever of you sights (the crescent on the first night of) the month (of Ramadan i.e. is present at his home), he must observe Sawm (fasts) that month, and whoever is ill or on a journey, the same number [of days which one did not observe Sawm (fasts) must be made up] from other days
So fasting is obligatory even at times when it is hot, because fasting Ramadan is one of the pillars of Islam. If a person fasts and then suffers intense thirst in which there is the fear that he may die, he may break the fast by drinking enough to keep him alive, then he should refrain from eating and drinking, and make up that day at another time. And Allah knows best.
And Allah is the source of strength. May Allah send blessings and peace upon our Prophet Muhammad and his family and Companions. End quote.
Standing Committee for Academic Research and Issuing Fatwas
Shaykh Abd al-Azeez ibn Abd-Allaah ibn Baaz, Shaykh Abd-Allaah ibn Ghadyaan, Shaykh Saalih al-Fawzaan, Shaykh Abd al-Azeez Aal al-Shaykh, Shaykh Bakr Abu Zayd
Reproduced from Islam QA