Take, for instance, the words prayer, almsgiving, fasting, and pilgrimage. Although most people understand these terms in a general way, none can grasp their precise, comprehensive, and exclusive definition except through the Messenger of Allah—may Allah bless him and grant him peace. Such terms are known as “legal names.”

Consider the funeral prayer, the prostration of forgetfulness, the prostration of gratitude, and circumambulation around the Ka‘bah. Do they fall under the Prophet’s saying, “The key to prayer is purification; its opening is the takbīr and its closing the salām”? In other words, are all these acts deemed “prayer” so that purification becomes obligatory for them, or is purification not required for some of them? Must purification be observed for every act whose sanctity is entered by the takbīr and exited by the salām—such as the funeral prayer and the prostration of forgetfulness—while it is not required for circumambulation or the prostration of recitation?

The same applies to terms like wine, usury, and gambling. Certain things that fall under these names are evident, while others remain unknown until additional clarification is given. An action may in fact be usury or gambling, yet a person may remain unaware of that until some proof—whether scriptural or otherwise—makes it clear.

Hence the Prophet’s response, upon him be peace, when he was asked about the limit of backbiting: “It is your mentioning your brother with something he dislikes.” Someone then asked, “What if what I say about my brother is true?” He replied, “If what you say is in him, you have backbitten him; and if it is not in him, you have slandered him.”

The same principle appears in his words: “No one who harbors even an atom’s weight of arrogance in his heart will enter Paradise.”