Praise be to Allah.
Fasting Ramadan is one of the pillars of Islam, and it is not permissible for an adult Muslim of sound mind who is accountable to break the fast in Ramadan except with an excuse, such as travelling, sickness and the like. Whoever breaks the fast – even for one day – with no excuse has committed a major sin and has exposed himself to the wrath and punishment of Allah. He must repent sincerely and make up the days that he did not fast, according to the majority of scholars; some of them narrated that there was consensus on this point.
Please see question no. 234125
As for the one who deliberately does not fast in Ramadan, thinking it permissible to do so, he has become a disbeliever. He should be asked to repent, and if he repents, all well and good, otherwise he is to be executed.
Whoever openly breaks the fast should be given a disciplinary punishment by the ruler, a punishment that will deter him and others like him from doing this grave act.
There follow a number of comments by the scholars concerning that.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
If a person breaks the fast in Ramadan, believing that to be permissible although he is aware of the prohibition on doing so, but he thinks that it is permissible for him, he must be executed.
If he is an evildoer, he should be punished for breaking the fast of Ramadan, as the ruler sees fit.
If he is ignorant, he is to be taught the ruling.
End quote from al-Fataawa al-Kubra (2/473)
Ibn Hajar al-Haytami (may Allah have mercy on him) said:
Major sins no. 140 and 141: Not fasting one of the days of Ramadan, and breaking the fast by having intercourse or otherwise, with no excuse such as sickness or travelling.
End quote from az-Zawaajir (1/323).
The scholars of the Standing Committee for Issuing Fatwas said:
Breaking the fast during the day in Ramadan on the part of one who is accountable is a major sin, if it is done without a legitimate excuse.
End quote from Fataawa al-Lajnah ad-Daa’imah (10/357).
Shaykh Ibn Baaz said:
Whoever breaks the fast on any day in Ramadan, with no legitimate excuse, has committed a grave evil. Whoever repents, Allah will accept his repentance, so he must repent to Allah sincerely, by regretting what he has done in the past and resolving not to repeat it, and he should ask his Lord for forgiveness a great deal, and hasten to make up the day that he did not fast.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked about the ruling on breaking the fast during the day in Ramadan with no excuse.
Breaking the fast during the day in Ramadan with no excuse is a major sin, and the individual becomes an evildoer thereby. He must repent to Allah and make up the day that he did not fast.
End quote from Majmoo‘ Fataawa wa Rasaa’il al’Uthaymeen (19/89).
An-Nasaa’i narrated in al-Kubra (3273) that Abu Umaamah said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: Whilst I was sleeping, two men came to me and took hold of my arms… And he quoted the hadith, in which he said: Then they set off with me, and I saw some people hung up by their Achilles tendon, with the corners of their mouths torn and dripping with blood. I said: Who are these? He said: These are the people who used to break the fast before it was permissible to do so.
Al-Albaani classed it as saheeh in as-Saheehah (3951), after which he said:
This is the punishment of those who fasted then broke the fast before the time for breaking the fast came. So how about those who did not fast at all?! We ask Allah to keep us safe and sound in this world and the hereafter. End quote.
For more information, please see the answer to question no. 38747
And Allah knows best.