Sources of Islamic law: The Qur'an, The Traditions of Prophet Muhammad (pbuh), Scholarly Consensus, and Deductive Reasoning.
[Taken from a brochure published by the Islamic Cultural Center in Tempe, AZ, USA]
The Qur'an:
Muslims believe the Qur'an is the exact word of God transmitted
through Angel Gabriel to Prophet Muhammad (peace be upon him). The Qur'an has not changed over the centuries. Originals dating back to the time of the third Caliph 'Uthman, who ruled just 20 years after
the death of Prophet Muhammad, can be found in Turkey, Britain, and Tashkent, a city in a former Soviet Republic.
The Qur'an is a book of Guidance. It is not in chronological or
thematic order. Rather, its style and rhythm is designed more like a
serious wake-up call that emphatically urges all humans to realize the
0 Power and Oneness of God, and live accordingly.
The exact word of Allah appears in the Arabic text. Thus, translations
are only approximate meanings of the original text. All Muslims, wherever they may reside, read the exact same Qur'an in Arabic. Millions of Muslims have memorized the entire Qur'an.
In fact, it is the most widely memorized and recited book in the
world.
The Qur'an has a unique style. It is not prose, nor is it poetry. The
Qur'an challenges poets and writers to create anything like it. For
over 1400 years no one has been able to meet this challenge. The Qur'an is filled with a variety of miracles, ranging from scientific miracles to linguistic miracles and more.
The traditions of Prophet Muhammad (peace be upon him) are called the sunnah, an Arabic term which means "path, or way of life". Thus, the Prophet Muhammad's way of life serves both as a model for Muslims and as a source of Islamic Law. The sunnah is comprised of hadith, which are the recorded sayings, actions and advice of the Prophet Muhammad.
Like all prophets, the actions of the Prophet Muhammad were inspired by Allah. Therefore, Muslims believe that the principles of the hadith are inspired by Allah.
The Qur'an orders Muslims to obey the commands of the Prophet Muhammad (peace be upon him). The Qur'an says: "So take what the Messenger assigns to you and deny yourself that which he nvithholdsEromyou." (59:7)
The sunnah gives detailed explanations of the broad principles mentioned in the Qur'an. For example, the Qurtan instructs, "Establish the service of worship", but doesn't specify exactly how to worship. By describing how the Prophet Muhammad (peace be upon him) prayed, the sunnah provides details on what the Qur'an instructed.
The consensus of Muslim scholars, called Ijma'a in Arabic, is used to make rulings about things not explicitly mentioned in the Quran or Sunnah.
Seeking the opinions of others on religious matters is sanctioned in the Qur an, where Allah says, "O ye who believe! Obey Allah, and obey the Messenger, and those charged with authority among you. If ye differ in anything among yourselves, refer it to Allah and the Messenger, if ye do believe in Allah and the last Day: that is best and most suitable for final determination." (Qur'an4:49)
The primary benefit of Scholarly Consensus is that it allows Muslim scholars to make legal rulings on issues not mentioned explicitly in the Qur'an or hadith, thus providing legal guidelines on a variety of modern day issues. This gives Islam the flexibility to be applicable in all times and places, and among all peoples.
All rulings based on the consensus of scholarly opinion must be derived from the teachings of the Qur'an and/or the instructions, teachings and actions of the Prophet Muhammad (peace be upon him).
Legal Precedent, or qiyas in Arabic, is a legal ruling arrived at through the process of analogical deduction or analogy. For example, the Qur'an prohibits the consumption of alcohol, but does not mention drugs. Based on reason (qiyas), drugs are also illegal in Islam because the common denominator, or reason for prohibition, is intoxication and harmful effects on health.