Are intrusive thoughts of doubt about the existence of God and thinking of abandoning prayer, despite trying to repel them and seeking refuge from them, considered apostasy?

By the grace of Allah, you are a Muslim with sound faith, and your aversion to these whispers is proof of the soundness of your faith. The Prophet, peace and blessings be upon him, informed the Companions that their dislike and repulsion of such whispers was clear faith. Continue to strive against them, certain that Allah will remove them, and know that you are upon goodness and more reward is hoped for you as long as you strive against them. Have a good opinion of your Lord, for death comes to the believer only with good.