Islamic legal system

law

peninsula worshiped idols. These tribes frequently fought with one another. Each tribe had its own customs governing marriage, hospitality, and revenge. Crimes against persons were answered with personal retribution
messenger Muhammad introduced a new religion into this chaotic Arab world. Islam affirmed only one true God. It demanded that believers obey God’s will and laws.
The Koran sets down basic standards of human conduct, but does not provide a detailed law code. During his lifetime, messenger Muhammad helped clarify the law by interpreting provisions in the Koran and acting as a judge in legal cases.

Quran, the Sunnat (the way the messenger Mohamed acted and his hadith which is rules and guidelines he said )
secondary sources are judicial decisions, customs and legislation
Sharia and fiqh are the science which is formed to study Quran and his laws so it helps to understand the rules of Islamic legal system

Muhammad ruled Arabia for about 30 years. These political-religious rulers, called caliphs continued to develop Islamic law with their own pronouncements and decisions.
Islamic law grew along with the expanding Muslim Empire. The Umayyad dynasty caliphs, who took control of the empire in 661, extended Islam into India, Northwest Africa, and Spain.

a brilliant legal scholar named Shafii systematized and developed what were called the “roots of the law.” Shafii argued that in solving a legal question
government judge should first consult the Koran. If the answer were not clear there, the judge should refer to the authentic sayings and decisions of Muhammad. If the answer continued to elude the judge, he should then look to the consensus of Muslim legal scholars on the matter. Still failing to find a solution, the judge could form his own answer by analogy from “the precedent nearest in resemblance and most appropriate” to the case at hand.

Sharia.
The brother, father or husband also had financial responsibility for his sister if she doesn’t have source of finance
A wife had the right to food, clothing, housing, and a marriage gift from her husband
After a divorce, the mother usually had the right of custody of her young children.
The support of an abandoned infant is a public responsibility.

Sharia can be adapted to modern conditions without abandoning the spirit of Islamic law or its religious foundations. Even in countries like Iran and Saudi Arabia, the Sharia is creatively adapted to new circumstances.
Some countries follow a mixture of sharia and legislation laws like Egypt