A typical paragraph:
8.0 APOSTASY FROM ISLAM
8.1 When a person who has reached puberty and is sane, voluntarily apostatizes from Islam, he deserves to be killed.
[Bukhari 9,83,17] Muhammad: “A Muslim who has admitted that there is no god but Allah and that I am His prophet may not be killed except for three reasons: as punishment for murder, for adultery, or for apostasy.”
The “08.1” is an index number in the Sharia law text, The Reliance of the Traveler. The text is divided into divisions— a, b, c, etc. This particular law is found in division 0; section 8; subsection 1. With the index number, 08.1, you can refer directly to the source which is The Reliance of the Traveler. In the example above we not only have the law, apostates (people who leave Islam) should be killed, but we have the supporting doctrine found in a hadith, a sacred text used along with the Qur’an. A hadith is what Muhammad did or said. This particular hadith is from Sahih al-Bukhari, one of the six canonical hadith collections of Sunni Islam.
These prophetic traditions, or hadith, were collected by the Muslim scholar Muhammad ibn Ismail al-Bukhari about 200 years after Muhammad died and compiled during his lifetime. It is the most authoritative of all the collections. Notice the index number— 9,83,17. This reference number is like a chapter and verse index so that you can go and read the original. All of the hadith, including Bukhari, can be found on many Internet sites. Go look at them yourself.
Here is a Sharia law supported by the Qur’an
Jihad means war against Kafirs to establish Islam.
Qur’an 2: 216 You are commanded to fight although you dislike it. You may hate something that is good for you, and love something that is bad for you. Allah knows and you do not.
Above, we have the Sharia text defining what jihad is and then the foundational reference for the authority is provided. Again, you can verify the accuracy of my statements about the Qur’an verses and the original reference, 09.0, in the Reliance of the Traveller by using it as a cross-reference. There is one last type of reference to a supporting document.