Kiisimu, Daleel maana yake ni ushahidi, dalili, au ushahidi wa kuthibitisha jambo. Kama istilahi, Daleel ni chanzo au ushahidi wa wazo, dhana, au hukumu fulani. Kila sheria au hukumu lazima iwe na Daleel, ambayo inaweza kutoka Qur'ani, Sunnah, au chanzo ambacho Qur'ani na Sunnah zimetuelekeza kukubali. Vyanzo hivi vitajadiliwa baadaye katika kitabu hiki. Hukumu yoyote kutoka katika maandishi ya Qur'ani au Sunnah inachukuliwa kuwa Daleel. Kwa mfano, Qur'ani inasema:

Linguistically, Daleel means a proof, indication, or evidence. As a term, Daleel means the source or evidence for a thought, concept, or a ruling. Any law or ruling must have a Daleel, which can be from Qur‟an, Sunnah, or a source, which Qur‟an and Sunnah directed us to adopt. These sources will be discussed later in the book. Any ruling from the text of either the Qur‟an or Sunnah is considered a Daleel. For example, the Qur‟an states:

Na iwepo miongoni mwenu kundi la watu wanaolingania kheri yote (Uislamu) na wanaoamrisha mema na kukataza maovu. (TMQ Al-Imran: 104)

“Let there arise out of you a group of people inviting to all that is good (Islam) and enjoining what is right and forbidding what is wrong.” (TMQ Al-Imran: 104)