Can a human being commit corruption while saying, "I am a Muslim"?

Faith consists of multiple branches, some of which, if lost, cause faith itself to be lost, such as the Oneness of Allah and believing in the Prophets and the Books, and denying what is known to be an indispensable part of the religion, like prayer and fasting. Some scholars even consider abandoning prayer an act of disbelief. Other branches, however, do not cause faith to be lost if they are absent. Fornication, theft, and drinking alcohol do not expel one from the fold of Islam unless one denies their prohibition, even though one's faith would be deficient and one would deserve punishment. Nevertheless, such a person will not abide eternally in Hellfire. Muslims are of different ranks: the highest among them are those who worship Allah as if they see Him, others commit minor sins that are expiated by good deeds, and some commit major sins for which Allah may grant forgiveness or punish them with a non-eternal torment. Sincere repentance expiates all sins.