What was the creed of the hypocrites who disbelieved after believing during the time of the Prophet, peace and blessings be upon him—was it polytheism (shirk) or atheism (ilhad)?

The hypocrite is one who conceals disbelief while outwardly displaying Islam. They are the worst and most dangerous type of evil people. Linguistically, hypocrisy (Nifaq) means to outwardly show Islam while inwardly concealing something else, and the technical meaning does not deviate from this. Hypocrisy may metaphorically be applied to one who commits a characteristic of practical hypocrisy, such as lying or breaking promises, but this is not the true, doctrinal hypocrisy.

Atheism, in its contemporary understanding, was not known in the Arabian Peninsula during the time of the Prophet, peace and blessings be upon him. Rather, people were either polytheists, Jews, or Christians. As for denying the existence of the Creator God, the Sustainer, it was unknown except among a very small number of materialists (Dahriyin). Hypocrisy emerged in Medina after the Muslims gained strength, and some polytheists and People of the Book engaged in it, outwardly displaying Islam while concealing disbelief. There were no hypocrites among the Muhajirun (emigrants). Hypocrisy means concealing disbelief and turning away from the religion of Islam, while outwardly displaying Islam contrary to what is in one's inner self, and there is no difference in this regard between different types of disbelief.