The official compilation of Hadith was initiated by 'Umar b. Abd al-Aziz, who was the eighth Umayyad caliph. He realized that the sayings and actions of Prophet Muhammad (peace be upon him) were not properly documented, and that some fabricated Hadiths were circulating among the people. In order to preserve the authenticity of the Prophet's teachings, 'Umar b. Abd al-Aziz ordered the scholars of his time to collect and authenticate the Hadiths. This process led to the development of the science of Hadith, which involved careful examination of the chains of narrators and the text of the Hadiths. The most famous compilation of Hadith is Sahih al-Bukhari, which was collected by Muhammad al-Bukhari in the 9th century, based on the standards set by 'Umar b. Abd al-Aziz and other early Hadith scholars.