What is "mihna"

The Miḥnah (, English: "trial" or "testing") refers to the period of religious persecution instituted by the 'Abbasid Caliph al-Ma'mun in 833 AD in which religious scholars were punished, imprisoned, or even killed unless they conceded the Mu'tazila doctrine of the created nature of the Qur'an. The policy lasted for fifteen years (833–848 CE) as it continued through the reigns of al-Ma'mun's immediate successors, al-Mu'tasim and al-Wathiq, and two years of al-Mutawakkil who reversed it in 848 (or possibly 851) AD.

The abolition of Mihna is significant both as the end of the Abbasid Caliph's pretension to decide matters of religious orthodoxy, and as one of the few instances of specifically religious persecution in Medieval Islam.