Who coined the terms "Mustahab" (desirable/recommended) and "Makrooh" (disliked/reprehensible) based on the criteria of reward and recompense, and what did they rely on from the Qur'an and Sunnah in doing so? And how did jurists differentiate between what is "Haraam" (forbidden) and "Makrooh," and what is "Waajib" (obligatory) and "Mustahab," especially in Hadiths that contain explicit commands and prohibitions?

The Usulis (jurists specialized in the principles of Islamic jurisprudence) have coined terms to differentiate between actions. They call an action where one is given a choice between doing it or leaving it, with a preference for doing it, "Mustahabb" or "Mandub" (recommended). When there is a preference for leaving it, they call it "Makruh" (disliked). This is to distinguish them from "Mubah" (permissible), "Wajib" (obligatory), and "Muharram" (forbidden). The basis of this terminology is the extensive study of religious texts and the differentiation between the types of divine commands. Where a divine command implies an action without indicating punishment for leaving it, it is a recommendation (Nadab); otherwise, it is an obligation (Ijab). When it implies leaving an action without indicating punishment for doing it, it is a dislike (Karahah); otherwise, it is a prohibition (Hathr).

The majority of scholars hold that a plain command, devoid of contextual indicators, implies obligation. They base this on the consensus of linguists and on Quranic verses such as: "And let those who oppose His command beware, lest a trial afflict them or there come upon them a painful punishment" (An-Nur 24:63), and prophetic traditions like his (peace be upon him) saying: "Were it not that I would overburden my Ummah, I would have commanded them to use the siwak with every prayer."

As for interpreting a command as something other than obligation (such as permissibility or recommendation) in certain texts, it is due to the presence of contextual indicators that divert it from obligation. Those who maintain that an absolute command implies obligation agree that it is only diverted from this meaning by a contextual indicator. However, they differ on the type of this indicator, falling into two schools of thought: The first holds that any strong contextual indicator can divert the command from obligation, whether it is a text, consensus, analogy, inferred meaning, or other. The second holds that the only contextual indicators that can divert a command from obligation are another text or a consensus.

Upon tracing the statements of jurists, it becomes clear that they interpret a command as an obligation unless there is a diverting contextual indicator or another evidence that contradicts the command. An example of this is the command of the Prophet (peace be upon him): "If one of you enters the mosque, he should pray two rak'ahs," which was diverted from obligation to recommendation by the majority due to the presence of contextual indicators, including the numerous texts stating that the obligatory prayers are five, and that anything beyond that is voluntary.