The knowledge which is deduced from the principles laid down in the Quran and Hadis by use of analogical deductions is known as Qiyas, which is The fourth source of Islamic law.
The root meaning of the word Qiyas is measuring or equality. It originates the fourth source of Islamic law from a verb that means to measure one thing by comparing it with another thing that is similar to it. It is the legal method that uses human reasoning to compare existing situations for which legislation already exists.
Such resort to reasoning has its origin in the conversation between the Holy Prophet PBUH and Mu’az bin Jabal, on his appointment as the governor of Yemen.
The Prophet PBUH is reported to have asked him. “How are you going to decide cases?” Mu’az answered: “By what is in the Book of Allah.”
The Prophet PBUH then asked: “And if you do not find anything therein to guide you?” “I will decide in the way the Prophet has been doing,” he answered.
The Prophet PBUH enquired, “But if you do not find any precedent from me, what then? will do my best by exercising my judgment,” Mu’az replied. The Prophet PBUH thereupon exclaimed: ”
Praise be to Allah, Who has so disposed of the delegate of His prophet as to be able to satisfy him.” (Abu Daud, Tirmizi)
According to another tradition, the Holy Prophet PBUH is reported to have told Abu Musa Ashari: “Judge upon the Book of Allah, if you do not find in it what you need, upon the Sunnah of the Prophet and if you do not find in that also, then use your personal opinion.” (Abu Daud, Tirmizi)
The Prophet PBUH himself relied on analogy in determining questions of law. For instance, he was once asked by a man, whose father though possessed of means, had died without performing pilgrimage, if it was necessary that it should be performed on behalf of the deceased, for the benefit of his soul. The Prophet PBUH replied: “What do you think you would do if your father died owing debt?” Here the argument is that the Prophet PBUH used the analogy of debt to show that an undischarged religious obligation of the nature of pilgrimage, should be performed by the heirs of a deceased person.
The companions of the Prophet PBUH also employed analogy for purposes of legal deductions and no one doubted its legality.
Qiyas or analogy was a principle of extension of Islamic law on the basis of a likeness in two situations, one of which was specially provided for in the Quran or Hadis. Thus, if the Quran prohibited the use of wine, the prohibition might be understood to include other intoxicants. As drugs like cocaine and opium were not known during the time of the Prophet PBUH, no mention has been made of them. However, the Prophet PBUH said: “Every intoxicant is Khamr, so every intoxicant is Haram. Since these drugs are highly intoxicating, they are also declared haram. The Quran asks us to give Zakat.
The Holy Prophet PBUH explained how it should be given. For example, for Zakat on goats, he said that one goat must be given out as 2 Lac for every forty goats. Giving a goat to a poor man would be of no use to him so he is allowed to sell the goat and give the money to him which would be of more use to him.
The Quran forbids sales transactions after the call for Friday prayers. By analogy, all kinds of transactions have been forbidden, because, like sales, they also distract Muslims from Friday prayers.
Another example is that of Wuzu, which is not valid even if the smallest portion of the body which has to be washed remains dry. According to water. tradition, reported by Hazrat Aisha, that if flour dries on the nails and considered has not reached any portion of that nail, Wuzu would not have been considered to have taken place. Going by this tradition, With the application of nail polish, Wuzu would be incomplete, as the nails remain dry.
It is admitted by Sunni jurists that the law for the guidance of Muslims in every matter is found either in the Quran or in the Hadis and Sunnah. They point out that laws on some questions have been laid down in clear terms but for some, the Quran gives indications from which inferences have to be drawn.
However, all agree that in matters, the answers to which have not been provided by a Quranic or a traditional text, nor determined by consensus of opinion, the law may be deduced from what has been laid down by any of these three authorities by the use of Qiyas. Qiyas is thus a source of law that is subordinate and subsidiary to the Quran, Hadis, and ijma. It must be applied only when there is no solution to this matter in the Quran or in the Hadis. It must not go pointed out that laws on some questions have been laid down in clear terms against the contents of the Quran or the principles of Islam, neither should it be in conflict with the traditions of the Holy Prophet PBUH.