Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa. – Fatwa No.6060
Fataawa Ramadhaan – Volume 2, Page 748, Fatwa No.759
Question: Is the one who does not fast, even though he is not ill or anything, become a disbeliever, despite performing his [obligatory] prayers?
Response: One who does not fast because he rejects it’s obligation then he is a disbeliever by consensus. As for one who does not fast because he is lazy and negligent then he does not become a disbeliever, however he is in great danger due to his leaving off a pillar from the pillars of Islaam upon which their obligation has been agreed.
And with Allaah lies all the success, and may Allaah send prayers and salutations upon our Prophet Muhammad ﷺ and his family and his companions.