Is fasting obligatory for Muslims?

Fasting is obligatory for a Muslim in several cases: fasting the month of Ramadan, as Allah Almighty says: "O you who have believed, decreed upon you is fasting," and the Prophet, peace and blessings be upon him, said: "Islam has been built upon five... and fasting Ramadan." This also includes making up for missed Ramadan fasts for those who are obligated to do so, and fasting for expiations, vows, and ransoms during Hajj for those upon whom any of these are obligatory. As for voluntary fasting, it has been explained previously.