Matters by which one enters Islam

Q: Is it sufficient to utter the first pillar, the testimony that there is no god but Allah and that Muhammad is the Messenger of Allah? Or is it necessary to have other things for a person's Islam to be complete?

A: If a disbeliever testifies that there is no god but Allah and that Muhammad is the Messenger of Allah with sincerity, certainty, and knowledge of what this testimony implies, and acts upon it, he enters Islam. Then he is required to perform the prayer and the rest of the rulings. This is why, when the Prophet (peace and blessings be upon him) sent Mu'adh to Yemen, he said to him: He did not command them to perform the prayer and pay the alms until after the oneness of Allah and faith in the Messenger (peace and blessings be upon him). If the disbeliever does that, he has the ruling of Muslims. Then he is required to perform the prayer and the other matters of the religion. If he refuses to do that, other rulings apply to him. If he abandons the prayer, the one in authority calls him to repent; if he repents, well and good, otherwise he is killed. And so it is with the rest of the rulings; he is dealt with according to what he deserves.