A harshen larabci, "Daleel" na nufin hujja, alama, ko shaida. A matsayin kalma ta ilimi, Daleel na nufin tushe ko shaida ga wani tunani, ra'ayi, ko hukunci. Duk wata doka ko hukunci dole ne ya kasance yana da Daleel, wanda zai iya kasancewa daga Alkur'ani, ko Sunnah, ko wata majiya da Alkur'ani da Sunnah suka umarce mu da karɓa. Za a tattauna waɗannan majiyoyi daga baya a cikin littafin. Duk wani hukunci daga nassin Alkur'ani ko Sunnah ana ɗaukarsa a matsayin Daleel. Misali, Alkur'ani ya ce:

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:

"Kuma a cikinku a samu wata al'umma da take kira zuwa ga dukkan abin da yake alheri (Musulunci) kuma take umurni da abin da yake daidai kuma take hana abin da yake munana."

“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)