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)

The Prophet (saw) showed Umar (ra) how to perform Qiyas by comparing the kiss of the fasting person to the rinsing of the mouth and showing that neither breaks the fast.13

The existence of an „Illah constitutes the common matter upon which comparisons take place. The following Hadith is another illustration of the concept of „Illah in Qiyas:

When the Messenger (saw) was asked about the trading of mature dates with dry dates, he asked: "Do the mature dates become lighter (in weight) if they dry up?" They said, "Yes." He said, "Then, no." (Daraqtuni)

Based upon the „Illah, the Prophet (saw) demonstrated Qiyas by extending the rule of Riba to trading mature dates with dry dates.

Ibn Abbas narrated, "A woman said, 'O Messenger of Allah, my mother died owing a vow to fast; should I fast for her?' He (saw) said:

“What if your mother owed a debt and you paid it back for her, would that settle it?‟ She said, 'Yes.' He replied, „Then, fast for your mother.‟” (Muslim)

Also, 'Abdullah ibn Zubair (ra) narrated:

"A man from Khath'an (a tribe) came to the Messenger of Allah (saw) and said, 'My father embraced Islam at an old age, and he cannot ride the camel and at the same time he is obligated to perform Hajj. Should I perform Hajj for him?' The Prophet (saw) said, 'Are you the eldest son?' He said, 'Yes.' The Messenger (saw) replied, 'What if your father owed a debt and you paid it back, would that settle it?' He said, 'Yes.' The Prophet (saw) said, 'Then perform Hajj for him.'" (Ahmad)

In both Ahadith, the Messenger instructed the Muslims how to draw the analogy between the debt of Allah in fasting and Hajj and the debt to a human being. Both of them share the same „Illah, which is the existence of a debt that must be paid. As the definition of Qiyas is derived from the Ahadith of the Prophet (saw), the definition is considered a Hukm Shari‟. The rule that is extracted through Qiyas is a Hukm Shari‟ that must be followed as any other Hukm Shari‟ extracted from other legislative sources. The definitions and general rules which are extracted from the evidences are themselves considered Ahkam Shar'iah.

Qiyas is established upon an „Illah, which is the common motive between any two issues. If an „Illah exists, then Qiyas can be performed otherwise Qiyas is not possible. According to the strongest opinion the „Illah must be stated or derived from a Shari‟ text. If this is the case, this Qiyas would be Shari‟ because the „Illah has been stated by a Shari‟ text. According to this view if this „Illah has not been stated or derived from a Shari‟ text, then the Qiyas cannot be considered valid from a Shari‟ perspective nor can it be considered as a valid daleel.

It is documented that the Sahabah used Qiyas in many instances. When Abu Bakr (ra) gave inheritance to the maternal grandmother and not the paternal one, some of the Ansar told him:

"You have given inheritance to a woman (the maternal grandmother) from a dead person (the grandson) who, if she were the dead person, he would not inherit from her. On the other hand, you left out a woman (the paternal grandmother) who, if she died, this person will inherit from her. So give them the one-sixth of the inheritance." When Abu Bakr heard this Qiyas, he changed his rule and established the new rule. In another example, Umar (ra) doubted applying the death penalty for the group that kills a person. Ali (ra) told him:

"O Ameer al Mu'mineen. If a group stole, would you cut their hands?" Umar said, "Yes," and Ali replied, "This is the same." Thus, Ali made Qiyas for the death penalty of a group based upon the penalty of theft for a group.

The evidence for Qiyas is the Shari‟ah texts which contain „Illah. The presence of an „Illah entails that we follow the rationale of the text (ma‟qool an-nass) of the Kitaab and Sunnah. Since the rationale is not from the mind but the text itself. If the rationale of the text extends to a new matter then we are obliged to extend it, otherwise we would not have followed the text.