The ruling on whoever only fasts and prays during Ramadhan.
Question :
If a person is active in fasting and praying only during Ramadhan, but he leaves off the prayer as Ramadhan ends, does he has a fast?
Answer:
The prayer is a pillar from the pillars of Islam, and it is the most emphasized pillar after the two Testimonies of Faith. It is from the mandatory duties upon the individuals, and whoever abandons it while rejecting its obligation or due to laxity and laziness, then he has disbelieved. In reference to those who fast Ramadhan and they only pray during Ramadhan, then this is an attempt to deceive Allâh. What wicked people these are who do not know Allâh except during Ramadhan. Thus, their fast is not acceptable while they are abandoning the prayer outside of Ramadhan.
Source:
The Permanent Committee
Fatawa Islamiyah, Vol. 3 Pages 247-248