What is the ruling on fasting for a person who observes fasting but does not pray? Does abandoning prayer affect the validity of his fast?

It is well established that all Muslims are required to perform all the religious obligations prescribed by Allah Almighty, so that they may attain the fullest measure of Allah’s pleasure and mercy, draw closer to Him, receive greater rewards, and have their deeds more readily accepted than those who perform some obligations while neglecting others. It also enables them to maintain a stronger bond with Allah Almighty. However, there is no interdependence between the discharge of one religious obligation and the neglect of another. Each obligation has its own reward, and each has its own punishment.

Whoever fasts but does not pray fulfills the obligation of fasting while bearing the sin of abandoning prayer, for which he will answer to Allah. There is no doubt that the reward of someone who fasts while fulfilling all the religious obligations and observing the limits prescribed by Allah is greater than that of someone who does not. The former fulfills his religious obligations and may hope to receive the fullest reward because of his strong relationship with Allah Almighty. As for the latter, his fasting serves only to discharge the obligation of fasting. He earns no additional reward unless Allah shows him mercy and encompasses him with His grace, generosity, and benevolence. In that case, it would be an act of divine grace and favor, rather than a reward or recompense attained through his own actions.

And Allah Almighty knows best.