The evidence from consensus to support the lawful use of Qiyas is the most important one for them. It is the one which they heavily rely. The consensus is that of the Suhabah, the people who are considered as companions of the holy Prophet.

As a matter of fact, they, the Suhabah, did use their opinion in a number of cases, even with the existence of the text of Shari’a. Were their practices based on Qiyas, the desirableness of the case or unspecified public interests is not clearly known. Were such practices interpretations of the texts, or due to lack of knowledge or simple disregard, some of such factors or all together, is not known.

Use of elaborate inference in the matters of Shari’a took greater technical shape in the second century. It was at this time that Qiyas, desirableness and unspecified public interest came to be considered as different forms of inference.

Of such practices one is the following decisions of ‘umar Ibn Al-khattab:

1. "There were two beneficial practices in the time of the holy Prophet and I announce them as prohibited and punish the violators (impermanent marriage and the interval between Hajj and ‘umrah."
2. Prayer in the form of Tarawih. (prayers in congregation during the month of Ramadhan besides the daily prayers.
3. Omission of one item from the call for prayer that said, "come to the best of deeds."

Were these decisions based on Qiyas or some other such factors are uncertain. The fact of the matter is that they were not based on technical form of Qiyas.

Ibn Hazm in his works, page 5, mentioned before writes, "Then they invented Qiyas in the second century, some of them accepted it and others rejected the same." In his book called Al-ahkam he writes, "An evil innovation emerged in the second century and it spread and became public in the third century Hijri. Apparently, His statements are against Qiyas. They are not against the decisions of Suhabah; therefore, Qiyas is different from their practices.

Al-ghazali in his book called Al-mustasfa’ vol. 2 p 58-62 mentions several instances of Suhabah’s using their opinions in the rules of Shari’a but he has not been able to prove such practices as inference in the form of Qiyas except that he has found no other way to justify such practices except by the justifying Qiyas which is due to his well wishing efforts, but, in fact, most of them do not fall under the category of Qiyas. It is the consensus of the Muslims and the companions that is considered as justifying Qiyas.

According to the Shi’a Muslim school of law the above kind of consensus never came into existence because of the following reasons:

1. The practices of the Suhabah such as those of ‘umar Ibn Al-khattab or Khalifa ‘uthman’s burning copies of the holy Quran were not based on Qiyas in its elaborate form.
2. The use of personal opinion, by some of the Suhaba, do not constitute consensus as Ibn Hazm has also agreed (see his works on Qiyas. Page 19)
3. One may ask, "How and where from did you find the consensus?" It is known that Suhabas were in thousands and all of them have not been able to give Fatwa (a qualified opinion about the rules of Shari’a) except for about one hundred thirty or so among them. Of these people only seven have many Fatwas, thirteen of them were of middle size in Fatwas and the rest had very few Fatwas, just on one or two cases besides the undeniable issue like daily prayers and fasting etc.
4. The point to make is not whether the Suhabah like Aba Bakr, ‘umar, ‘uthman and Zayd Ibn Thabit, give Fatwas on the basis of their own opinions or not. The point to make is that how such practices could be considered consensus of all Muslims? In fact, agreement of ten, or even twenty does not constitute consensus no matter which ones they may happen to be.

All that could be said is that since the others remained silent and this is considered as their consent and confirmation, thus, consensus is formed?

 The problem that still remains with the above argument is that silence could come into being for a number of reasons.

The only silence that counts is the silence of an infallible person with the existence of the conditions for ‘iqrar which means confirmation; and consent

 Silence in itself is ambiguous and silence by non-infallible may take place due to:

 1. It can take place because of fear.

2. It can take place because of shyness.

3. It can be because of lack of courage.

4. Flattery can also cause silence.

5. It can take place because of lack of concern about the truth.

6. It may happen because of the ignorance of the rule of Shari’a etc.

More than one such reason may become the cause for one’s silence in the support of the truth.

 (e) As a matter of fact, the silence of the others is not an established fact. Only the silence of one person who is qualified to issue a Fatwa is enough to invalidate the consensus. Consensus means the agreement of all. If this would be the case just because of one persons’ disagreement then what would one think of the disagreement of more than one person.

 It is well known that Ibn Mas’ud, Ibn ‘abbas and others expressed strong protest and disapproval of using personal opinion in matters of Shari’a.

 It is narrated that even ‘umar said this against the use of ones’ opinion in matters of Shari’a, "Beware of the people who use their own opinion because they are the enemies of the Sunnah. They have become tired of memorizing the Ahadith, thus, they use their opinion that lead them astray or cause others to go astray." From the works of Ibn Hazm and Al-ghazali.

It is very possible that this statement is forged against him.

That he was very much interested in the use of his own opinions in the matters of Shari’a there is a good deal of evidence to support it. This is besides the fact that the style of the statement does not match those of his time.

There is nothing more destructive to the establishment of consensus than publicly opposing and issuing opposite Fatwas. This, actually did happen with Ibn Mas’ud and Ibn ‘abbas to the limit of invocations against each other and warning against the wrath of God for the use of personal opinion in the matters of Shari’a. How can in such conditions consensus be established?

For the Shi’a Muslims the disagreement of Imam Ali (peace be up on him) with the use of personal opinion in the matters of Shari’a is more than enough. He is an infallible person and in the words of the holy Prophet truth moves hand in hand with Imam Ali, peace be upon them. It is narrated from Imam Ali who said, "If use of personal opinion would have been acceptable then whipping of the top of feet would have had greater priority than their bottom."