Fasting is one of the five pillars of Islam. The precise definition of a pillar also known as rukn (in Arabic) is “that without which the thing itself is not there.” An example in daily life would be a house. A house is usually built upon pillars which support its roof, if one of them is not there then the house does not stand alone or in other words does not exist. <>

Similarly without as siyaam (fasting) there is no Islam or Islam is not complete. This is derived from the hadeeth of the Prophet (saw) narrated by Ibn ‘Umar (r.a) who said that Allah‘s Apostle said, “Islam is based on (the following) five (principles): To testify that none has the right to be worshipped but Allah and Muhammad is Allah‘s Apostle; to offer the (compulsory congregational) prayers dutifully and perfectly; to pay Zakat (i.e. obligatory charity); to perform Hajj. (i.e. Pilgrimage to Mecca); to observe fast during the month of Ramadhan.”

Therefore every Muslim has to fast and one who denies one of the pillars of Islaam, he has no Islaam, and has chosen a way of life other than Islaam. And as Allah has said in the Holy Quraan:

وَمَن يَبْتَغِ غَيْرَ الإِسْلاَمِ دِينًا فَلَن يُقْبَلَ مِنْهُ وَهُوَ فِي الآخِرَةِ مِنَ الْخَاسِرِينَ

And whoever seeks a religion other than Islaam, it will never be accepted of him, and in the Hereafter he will be one of the losers.[Surah Aal Imran (3) V. 85]