Q 32: What is the textual proof that Sawm (Fasting) is obligatory?
A--- Allah, the Almighty says: {O you who believe! Observing As-Sawm (the Fasting)(12)
Is prescribed for you as it was prescribed for those before you). (Al-Baqarah, 183)
Allah says: {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}. (Al-Baqarah, 185)
According to a Hadith, a Bedouin said to Allah's Messenger (Peace be upon him): Tell me the Fast that Allah makes obligatory for me. He (Peace be upon him) said: "The month of Ramadan. The inquirer said:
Am I obliged to fast anything else besides this? He (the Prophet (Peace be upon him)) said: No, except that which you observe out of your own free will". (Sahih Bukhari)
(12) As-Sawm means Fasting i.e. not to eat or drink or have sexual relations etc. from the Adhan of the Fair (early morning) prayer till the sunset. (Translator)
Reference: 200 FAQ On Muslims Belief - Shiekh Hafiz Ibn Ahmed Al Hakami