Yet some people insist on saying, “Ribā (usury) is the gravest of the forbidden acts, zina (fornication) is the gravest of the forbidden acts.” As a result, they devote all their efforts to condemning ribā, zina, and moral corruption, while showing no concern for shirk and issuing no warning against it—even though they see people actually committing it. Such an attitude betrays profound ignorance of Allah’s law.

The greatest thing Allah has forbidden is shirk. It is more serious than ribā, more serious than drinking wine, more serious than theft, more serious than unlawfully consuming people’s wealth, and more serious than gambling and games of chance—it is the gravest of all prohibitions. The proof is Allah’s statement:

“Say, ‘Come, let me recite to you what your Lord has forbidden for you: that you associate nothing with Him; that you show kindness to parents; that you do not kill your children out of poverty—we provide for you and for them; that you do not approach shameful deeds, whether open or secret; and that you do not take a life that Allah has made sacred, except by right. This is what He has enjoined upon you so that you may understand. And do not approach the property of the orphan except in a way that is best…’” to the end of the verses (al-Anʿām 6:151–152).

These verses are known as the Ten Commandments: “Say, ‘Come, let me recite to you what your Lord has forbidden for you…’” up to His words, “This is what He has enjoined upon you so that you may understand” (al-Anʿām 6:151–152).