Abu Dawud al-Sijistani travelled from 835 to 856 collecting Hadith narrations in Khurasan, Baghdad, Basra, Mecca, Kufa, Syria, the Byzantine frontier, and Egypt. He then spent about ten years sifting through the approximately 500,000 Hadith he collected to compile Sunan Abu Dawud, today considered one of the six most important collections of Hadith.