Does doubt about Islam invalidate prayer and good deeds?

A Muslim must protect their religion and heart from doubts and suspicions that lead to deviation. It is not permissible for one who is not armed with religious knowledge to debate with atheists, to avoid being deceived by their specious arguments. The early Muslims warned against accompanying people of innovation. A Muslim should seek religious knowledge to strengthen their faith and certainty in the truth of Islam and the word of Tawhid (definition), in accordance with His, the Almighty’s, saying: "The believers are only those who have believed in Allah and His Messenger and then doubt not but strive with their properties and their lives in the cause of Allah. It is those who are the truthful," and His saying about the hypocrites: "and their hearts have doubted, so they are in their doubt, wavering." If fleeting thoughts do not settle in the heart and one does not speak of them, they do not take one out of the fold of Islam.