After numerous collections of Hadith had been made during the third century of Islam six works became recognised as authoritative. Two of them are believed to be completely authentic, namely the Sahih al-Bukharii and the Sahih Muslim. The other four, Sahih al-Tirmidhi, Sunan Ibn Majah, Sunan Abu Dawud and Sunan Nasa'i are also highly esteemed but are regarded lower in category to Sahih Bukhari and Muslim