The evidence that Qiyas is a source of Shar'iah is that the „Illah is based upon or derived from a Shari‟ text. These Shari‟ texts are the Quran, the Sunnah, or Ijma' as-Sahabah. These three have been proven as definitive sources of Shari‟ah upon which no one can disagree upon. Therefore, the evidence that the „Illah exists in the text in general is definitive (Qata‟i) and this is also the case for Qiyas. When a text mentions a reason for a rule, extending this rule to any other issue having the same reason is considered another application for the text of the Ayah or Hadith.

The Prophet (saw) demonstrated Qiyas and considered it as a Shari‟ Daleel. The Sahabah followed him in this regard, and they also considered Qiyas as a Shari‟ Daleel to extract rules. The Prophet (saw) said to Mu'adh and Abu Musa al-Ashari when he appointed them as judges in Yemen:

“What will you judge with?” They said, “If we do not find the rule in the Book or the Sunnah, we will compare the unknown issue with the known issue, and we will apply it.” (Ihkam of Amidi)

The Prophet (saw) also demonstrated Qiyas in the following Hadith: The Messenger (saw) said to a Sahabiyah when she asked regarding making Hajj on behalf of her father, "If your father owed a debt and you paid it for him, would that suffice?" She said, "Yes." He said, "The same is for the debt of Allah."12

In order to instruct the Muslims, the Prophet (saw) showed the Muslims how to compare the debt owed to Allah to that owed to a human being, such that paying it back fulfills the obligation. Thus, the rule confirms the acceptance of the settlement of the debt. On the other hand, the rule of the known Hukm may be one of negation. For example, Umar (ra) asked the Prophet (saw) regarding whether or not the kiss of a fasting person would break the fast. The Messenger (saw) said: "What if you rinse your mouth, does that break the fast? He replied „No‟" (Ahmad)