The Kutub al-Sittah are six (originally five) books containing collections of hadith (sayings or acts of the prophet Muhammad) compiled by six Sunni Muslim scholars in the ninth century CE. They are sometimes referred to as Al-Sihah al-Sittah, which translates as "The Authentic Six". They were first formally grouped and defined by Ibn al-Qaisarani in the 11th century, who added Sunan ibn Majah to the list. Since then, they have enjoyed near-universal acceptance as part of the official canon of Sunni Islam.