For this reason, the foundation of Islam is “the testimony that none has the right to be worshipped but Allah.” This entails worshipping Allah alone and abandoning the worship of all else. This is Islam in its universal sense, besides which Allah accepts no religion from earlier or later generations. As He, exalted is He, says:

“Whoever seeks a religion other than Islam, it will never be accepted from him, and in the Hereafter he will be among the losers.”

And He, exalted is He, says:

“Allah bears witness that there is no deity worthy of worship except Him, as do the angels and those endowed with knowledge. He upholds justice. There is no deity worthy of worship except Him, the Almighty, the All-Wise.”

“Indeed, the religion in the sight of Allah is Islam.”

What we have mentioned makes clear that the true foundation of religion consists of inward knowledge and deeds, and that outward deeds are of no benefit without them. As the Prophet—may Allah bless him and grant him peace—said in the hadith narrated by Ahmad in his Musnad:

“Islam is outward, while faith is in the heart.”

For this reason, the Prophet—may Allah bless him and grant him peace—said in the hadith reported by both al-Bukhārī and Muslim, on the authority of al-Nuʿmān ibn Bashīr, who narrated from the Prophet—may Allah bless him and grant him peace:

“What is lawful is clear, and what is unlawful is clear. Between them are doubtful matters of which many people have no knowledge. Whoever avoids doubtful matters safeguards his honour and religion, while whoever falls into doubtful matters falls into the unlawful, like a shepherd grazing his flock around a protected pasture, on the verge of entering it. Indeed, every king has a protected domain, and Allah’s protected domain is what He has forbidden. Indeed, within the body is a morsel of flesh: when it is sound, the rest of the body is sound, and when it is corrupt, the rest of the body is corrupt. Indeed, it is the heart.”

Abū Hurayrah said: “The heart is a king, and the limbs are its soldiers. When the king is good, its soldiers are good; when the king is corrupt, its soldiers are corrupt.”