What is the difference between an emphasized Sunnah (Sunnah Mu'akkadah) and a supererogatory act (Nafl), knowing that both are voluntary acts for which a person is not sinful for abandoning?

Acts of worship are divided into two types: obligatory (fard) and supererogatory (nawafil). Jurists (fuqaha') have differed on the terminology for supererogatory acts (sunnah, mustahabb, mandub, tatawwu') across three opinions:

1. Synonymity: The terms are synonymous. This is the well-known view among the Shafi'is, while acknowledging that some sunnah acts are more emphasized than others.

2. Generality: Nafil (supererogatory) is a more general term that includes sunnah and mustahabb. This is the view of the Hanafis.

3. Distinction: Nafil is what the Prophet, peace be upon him, did but did not persist in. Sunnah is what he persisted in and performed openly in congregation. This is the madhhab of the Malikis and Hanbalis, who categorized mandub (recommended) into sunnah, fadilah (virtue), and nafilah.

The Hanafis believe that one who abandons an emphasized sunnah (sunnah mu'akkadah) commits a sin, but their sin is less than that of one who abandons an obligatory (wajib) act.

In summary: Anything beyond the fard (obligatory) and wajib (compulsory) is called sunnah, mandub, mustahabb, raghibah, or fadilah. These are of varying ranks, and the most emphasized among them is what the Prophet, peace be upon him, consistently practiced and performed in congregation.