The ruling on the Person who fasts but is lazy about performing the Prayer

Question :

Some of the young men - may Allah guide them - are lazy about performing the prayer during Ramadhan and other times. However, they strictly guard the fast of Ramadhan, while patiently bearing the thirst and hunger. What do you advise them and what is the ruling on their fast?

Answer:

My advise for these people is that they contemplate for a while about their situation and that they should know that the prayer (As-Salah) is the most important pillar of Islam after the two Testimonies of Faith. They should know that whoever does not pray, and he abandons the prayer due to being lax about it, then according to the correct view with me, that is supported by the proof of the Book and the Sunnah, he is a disbeliever. His disbelief is that which expels him from the religion as an apostate from Islam. Therefore, the matter is not light, because whoever is a disbeliever, who has apostatized from Islam, no fast or charity is accepted from him. No deed is accepted from him at all. This is due to the Statement of Allâh, the Most High:
"And nothing prevents their contributions from being accepted
from them except that they disbelieved in Allah and in His Messenger (Muhammad), and that they do not come to As- Salah (the prayer) except in a lazy state, and that they do not offer contributions except unwillingly."

Thus, Allâh explained that their contributions, even though they contain considerable benefit for others, are not accepted from them with their disbelief. And He, the Most High said:
"And We shall turn to whatever deeds they (disbelievers, polytheists, sinners) did, and We shall make such deeds as scattered floating particles of dust."

These people who fast and do not pray, their fast is not accepted. Rather, it is rejected as long as we say that they are disbelievers, as the Book of Allâh and the Sunnah of His Messenger prove. Hence, my advice to them is that they fear Allah, the Mighty and Majestic, and that they guard the performance of the prayer. They should pray them in their times and with the congregation of the Muslims. If they do so, I guarantee for them, by the Power of Allâh, that they will find in their hearts a firm desire in Ramadhan and other months to offer the prayer in its times with the congregation of the Muslims. This is because if the human being turns to his Lord, comes to Him and sincerely repents to Him, then he will be better after the repentance than he was before it. This is as Allâh mentioned concerning Adam, that after what happened with him of eating from the tree, Allâh said:
"Then His Lord chose him, and accepted his repentance, and gave kim guidance."

Source:
Ash-Shaykh Ibn 'Uthaimin
Fatawa Islamiyah, Vol. 3 Pages 245-246