What is the sunction of those muslim people observing prayer five times a day but not fasting?
The Ramadaan fast is one of the pillars on which Islam is based. Al-Bukhaari (8) and Muslim (16) narrated that Ibn 'Umar (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Islam is built on five (pillars): the testimony that there is no god except Allaah and that Muhammad is the Messenger of Allaah; establishing regular prayer; paying zakaah; fasting Ramadaan, and performing Pilgrimage to the House (the Ka’bah).”
Whoever does not fast has abandoned one of the pillars of Islam and has committed a grave major sin. In fact, some of the salaf were of the view that such a one is a kaafir and an apostate – Allaah forbid.
Al-Dhahabi (may Allaah have mercy on him) said in al-Kabaa'ir (p. 64):
The believers are unanimously agreed that whoever forsakes the Ramadaan fast when he is not sick and has no other excuse for that is worse than an adulterer or one who is addicted to alcohol. They doubt whether he is a Muslim and they think of him as a heretic and deviant. End quote.
Shaykh Ibn 'Uthaymeen (may Allaah have mercy on him) was asked about the ruling on breaking the fast during the day in Ramadaan for no legitimate reason.
Breaking the fast during the day in Ramadaan for no legitimate reason is one of the worst of major sins, because of which a person may be regarded as a faasiq (disobedient, rebellious) who has to repent to Allaah and make up the day when he broke the fast. I.e., if he fasted then during the day he broke his fast with no excuse, he has committed a sin, and he has to make up that day because when he started that fast, it became binding on him to complete it, so he has to make it up, like a vow. But if he did not fast at all, deliberately and with no excuse, then the correct view is that he does not have to make it up, because that will not benefit him at all, as it will never be accepted from him. The basic principle with regard to acts of worship that are connected to specific times is that if a person delays them beyond that specific time with no excuse, they will not be accepted from him, because the Prophet said: "Whoever does a deed that is not in accordance with this matter of ours, will have it rejected." And because it is a transgression of the sacred limits of Allaah, may He be glorified and exalted, and transgressing the sacred limits of Allaah is zulm (wrongdoing), and no deeds are accepted from the zaalim (wrongdoer). Allaah says (interpretation of the meaning):