I prayed behind someone for about eight months but later discovered that he is a sponsored christian who has some knowledge of Islam. He was never muslim. What is the status of the prayers that I prayed behind him?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.

According to the opinion of most scholars, your prayers behind this Christian man are invalid and it is incumbent on you to repeat them. However, some scholars held that if you did not know that he was non-Muslim then your prayers are valid. This view was adopted by Ibn Hazm and Shaykh Ibn ʻUthaymeen inclined to this view as well.

It should be noted, though, that it is better and more prudent in terms of clearing yourself of your liability to repeat these prayers that you performed behind this Christian man; you should perform them according to your ability in a way that does not cause harm to your body or livelihood. Please, refer to fatwa 105182.

Allaah knows best.