Sawm is wajib/fard (compulsory) on Muslims, according to the Qur’an and Sunnah (tradition of the Prophet), during the night month of the Hijri calendar, called Ramadan.

Allah, the Most High, said in the Qur’an, “The month of Ramadan in which was revealed the Qur’an, a guidance for mankind and clear proofs for the guidance and the criterion (between right and wrong). 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,…”
O you who have believed, decreed upon you is fasting as it was decreed upon those before you that you may become righteous – Al Baqarah:183 (source: quran.com).

Download Full Version

References:
http://yushaevans.com
http://askaquestionto.us
http://quran.com
http://www.myot.org.au
http://www.fastramadan.com
http://sunnah.org
http://www.sunniforum.com