A lot of Islamic history lies in the forms of hadith: Oral tradition passed down through several people. Wikipedia is a little misleading on the description, the term is used for almost all oral tradition in the Islamic world that has been written down, not just Muhammad. It is also used for anyone who may be termed a religious figure, like caliphs.
They are often written in the form of:
Narrated Al-Bara bin Azib:
Allah's Apostle sent a group of persons to Abu Rafi. Abdullah bin Atik entered his house at night, while he was sleeping, and killed him.
A weaker hadith would narrate several chains as in "Ali narrated that Omar said that Ali ibn Ali heard Muhammad PBUH say..."
There are various levels of reliability.. A "sahih" (translated: "correct") hadith would attempt to verify everyone down the narration chain and be considered "sahih" if all the narrators in a chain were considered reliable, and if there are other similar narrations that agree to the same thing. Because they bear religious significance, a lot of care is put into verifying them, but then again, there are many attempts to falsify a hadith depending on which sect you ask.
Wikipedia allows their use extensively, such as in http://en.wikipedia.org/wiki/List_of_expeditions_of_Muhammad
Nearly all of Islamic record keeping before the 10th century would be in the form of hadiths or Quranic text. If there is a book written on the subject, the primary sources will often be formed from hadiths as well.
However, the controversy would lie in that they're considered religious text, and people who don't consider any religious scripture valid would immediately consider a hadith invalid. It's not a major issue if so... pre-10th century Islam/Middle East questions could be moved to Islam SE instead, who are happy to debate the validity of sources.
