The revealed word of Islam, the Qur'an, in a formal Arabic which became more archaic with time, required explication. The Sunna, the spoken and acted example of the Prophet, collected as hadith, is an important traditional source that is used to supplement and explicate the Qu'ran. The Sunna is almost as important to Islam as the Qur'an, for in it lie the elaborations of Qur'anic teaching essential to the firm establishment of a world religion. There are disagreements in the hadith, and aspects of interpretations of the Qur'an and the Sunna have varied so much as to be contradictory at times. These situations are resolved by reference to one of the most important of the sayings attributed to the Prophet, "My community will never agree in an error." This leeway also allowed Islam to expand by incorporating social, tribal, and ethnic traditions. For example, with the exception of inheritance and witness laws, Islamic rights and obligations apply equally to men and women. The actual situation of women is more a function of particular social traditions predating Islam than of theoretical positions. For more information on Islamic law, see sharia; for discussions of the major branches of Islamic theology, see Shiite, Sunni.