Salam Ramadhan Al Mubarak...

The obligation of fasting on the believers is known from the Qur'an and the Hadith. It was explicitly stated in Verse #183 of Surah Al-Baqarah:

which means "O Belivers,Fasting is an obligation upon you as it was obligated upon the (Muslims) before you, so it would help you to reach piety"

Fasting was an obligation on the nations before the nation of Prophet Muhammad, however, fasting the month of Ramadan in particular is a specification only for the nation of Prophet Muhammad.

Fasting the month of Ramadan is an obligation and a great worship. It is among the best acts of obedience and greatest deeds, and one for which there is great reward. Imam al-Bukhariyy related the Qudsiyy hadith that the Prophet said Allah said: which means: "The reward of every good deed is multiplied ten up to seven-hundred times, except that of the Fasting; it is usually done in sincerity and will be multiplied by as many times as Allah wills."

One of the doors of Paradise, named ar-Rayyan, is specified for those Muslims who used to fast in this world. On the Day of Judgment, it will be opened, and those who used to fast in obedience to Allah enter through it, then it would be closed and no others will enter through it.

The month of Ramadan is the ninth month of the lunar year. It is the best month of the year, as is the night of al-Qadr in Ramadan the best night of the year. Fasting became an obligation on the Muslims in the second year after the emigration. Prophet Muhammed fasted nine years of Ramadan after which he died.

Moreover, Prophet Muhammad named Fasting (the month of Ramadan) as one of the five most important matters of Islam in the famous hadith known as Hadith Jibril related by al-Bukhariyy and Muslim. Angel Jibril came to the Prophet in the shape of a man with white clothes and asked him to inform him about Islam. In response, the Prophet said:

which means: "Islam is to bear witness that no one is God except Allah and that Muhammad is the Messenger of Allah, performing Prayer, paying Zakat, performing Pilgrimage if you are able, and Fasting the month of Ramadan. "

Consequently, renouncing the obligation of fasting the month of Ramadan, for the one who has learned of its obligation, is blasphemy because it entails belying Allah and the Prophet. The one who believes it is an obligation, however, does not perform this obligation (without a valid excuse) does not blaspheme--rather he is an enormous sinner.

Allah knows best.