The two main sources of Islamic finance which are based on the sharia law are the Qur'an and the Sunna. The Qur'an is the holy book, and the sunna is the body of knowledge derived from the teachings of the Prophet Muhammad as preserved in the Hadith literature. Other sources include Ijtihad, which contains legal interpretations, and Ijma, a text of agreed principles by all and is not open to interpretation.