Shaykh Abū ʿAmr ibn al-Salāh said:

Concerning the Prophet’s words, may Allah bless him and grant him peace, “Islam is that you testify that there is no deity worthy of worship except Allah,” and the rest of the passage, and “Faith is that you believe in Allah, His angels, His Books, and His messengers,” and the rest of the passage, he said:

This explains the foundation of faith, namely inward affirmation, and the foundation of Islam, namely outward submission and compliance. Outwardly, a person’s status as a Muslim is established by the two testimonies of faith. He mentioned the four alongside them only because they are Islam’s most manifest and principal rites. By performing them, a person completes his submission; abandoning them suggests that he is undoing the bond of his compliance, or that it is coming undone.

The term faith also encompasses the practices used to explain Islam in this hadith, as well as all other acts of obedience, because they are fruits of inward affirmation—which is the foundation of faith—and serve to sustain, complete, and preserve it. Thus, in the hadith of the delegation of ʿAbd al-Qays, the Prophet, may Allah bless him and grant him peace, explained faith as the two testimonies, prayer, zakat, fasting, and giving one-fifth of the spoils of war.

For this reason, the unqualified designation “believer” does not apply to someone who commits a major sin or neglects an obligatory duty. A designation denoting completeness applies to the complete instance and is not ordinarily used for a deficient one without qualification. It was therefore permissible to deny him this designation without qualification in the Prophet’s words, may Allah bless him and grant him peace:

“The adulterer is not a believer while committing adultery.”

The term “Islam” also encompasses the “foundation of faith,” namely affirmation, and the “foundation of acts of obedience,” for all of this is submission.

He said: From what we have explained and established, it follows that Islam and faith overlap in some respects and differ in others, and that every believer is a Muslim, but not