Ibn Kullab () (d. ca. 241/855) was an early Sunni theologian (mutakallim) in Basra and Baghdad in the first half of the 9th century during the time of the Mihna and belonged, according to Ibn al-Nadim, to the traditionalist group of the Nawabit. His movement, also called Kullabiyya, merged and developed into Ash'arism, which, along with Maturidism and Atharism (practically: Hanbalism), forms the theological basis of Sunni Islam.
Ibn Kullab headed a group made up of mainly direct and second generation students of Al-Shafi that included Al-Karibisi, Al-Qalanisi, Al-Muhasibi, Al-Bukhari, Abu Thawr and Dawud-al Zahiri. They were known for their extreme criticism of Jahmis, Mu'tazilis, and Anthropomorphists by using rationalistic methods (Kalam) to defend orthodox creedal points of Sunni Islam. They contradicted the Mu'tazili doctrine of Khalq al-Qur'an (Createdness of the Qur'an) by introducing a distinction between the words of God (Kalam Allah) and its pronunciation.
He was praised by several famous scholars, including Ibn 'Asakir, Taj al-Din al-Subki, Ibn Hajar al-'Asqalani, Ibn Khaldun, Ibn Abi Zayd al-Qayrawani, , Jamal al-Din al-Isnawi, in his , Abu Mansur al-Baghdadi in his work , al-Shahrastani in al-Milal wa al-Nihal, and al-Kawthari.
Abu Muhammad 'Abdallah ibn Sa'id ibn Kullab al-Qattan al-Basri al-Tamimi.
He belonged to the generation of Ahmad ibn Hanbal and Ishaq ibn Rahwayh. His precise year of birth is unknown, but he lived in the period of the 'Abbasid caliph al-Ma'mun.
It has been said that Dawud al-Zahiri, al-Bukhari and al-Harith al-Muhasibi learned kalam from him, according to al-Dhahabi in his . It has been reported also that al-Junayd al-Baghdadi was one of his students.
He has a number of works that are documented such as:
These books are lost, however remnants of them can be found in other works such as Maqalat al-Islamiyyin of Abu al-Hasan al-Ash'ari. He was also quoted by the early Ash'ari scholars such as Ibn Furak (d. 406H).
He died in 240 AH, or according to some in 241 AH.