All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Asking this man about his wife – be she an atheist or not – does not render you a disbeliever. Reviewing some of your previous questions, we realized that you are suffering from whispers, so turn away from them and seek refuge with Allah from them.
Besides, you should know that if a person’s Islam is proven with certainty, then it cannot be overruled except with a similar certainty.
So, none is judged as a disbeliever based on suspicion.
If the said man is married from an atheist woman, you should gently advise him or ask some of his close friends to encourage him to make her repent to Allah. So, if she repents, praise be to Allah; in which case, the husband must renew the marriage contract because the first contract is initially null and void, since the woman is a non-Muslim. But, if she insists on her atheism, you should tell him that it is forbidden for him to stay with her and he should hurry to forsake her. Allah Says (what means): {And hold not to marriage bonds with disbelieving women.} [Quran 60:10]
Allah knows best.