Mihna in the context of Mu'tazilism

Abū al-ʿAbbās Abd Allāh ibn Hārūn al-Maʾmūn (Arabic: أبو العباس عبد الله بن هارون الرشيد, romanized: Abū al-ʿAbbās ʿAbd Allāh ibn Hārūn ar-Rashīd; 14 September 786 – 9 August 833), better known by his regnal name al-Ma'mun (Arabic: المأمون, lit. 'the Reliable'), was the seventh Abbasid caliph, who reigned from 813 until his death in 833. His leadership was marked by the power and prosperity of the Abbasid Caliphate, al-Ma'mun promoted the Graeco-Arabic translation movement, the flowering of learning and the sciences in Baghdad, and the publishing of al-Khwarizmi's book now known as "Algebra", making him one of the most important caliphs in the Islamic Golden Age. He is also known as a proponent of the rational Islamic theology of Mu'tazilism.

Al-Ma'mun succeeded his half-brother al-Amin after a civil war, much of his reign was spent on peace campaigns. His strong support for Mu'tazilism led him to imprison a Sunni Imam, Ahmad ibn Hanbal in an event that became known as mihna. Al-Ma'mun's foreign policy was due to his decision to continue war and diplomatic relations with the Byzantine Empire, the tension between conflict or diplomacy varying during his military campaigns.

Abū ʿAbd Allāh Muḥammad ibn Ismāʿīl ibn Ibrāhīm al-Juʿfī al-Bukhārī (Arabic: أبو عبد الله محمد بن إسماعيل بن إبرهيم الجعفي البخاري; 21 July 810 – 1 September 870) was a 9th-century Muslim muhaddith who is widely regarded as the most important hadith scholar in the history of Sunni Islam. Al-Bukhari's extant works include the hadith collection Sahih al-Bukhari, al-Tarikh al-Kabir, and al-Adab al-Mufrad.

Born in Bukhara in present-day Uzbekistan, Al-Bukhari began learning hadith at a young age. He travelled across the Abbasid Caliphate and learned under several influential contemporary scholars. Bukhari memorized thousands of hadith narrations, compiling the Sahih al-Bukhari in 846. He spent the rest of his life teaching the hadith he had collected. Towards the end of his life, Bukhari faced claims the Quran was created, and was exiled from Nishapur. Subsequently, he moved to Khartank, near Samarkand.

Ahmad ibn Hanbal (Arabic: أحمد ابن حنبل, romanized: Aḥmad ibn Ḥanbal; (164-241 AH; 780 – 855 CE) was an Arab jurist and founder of the Hanbali school who is widely recognized as the scholar who memorized the most Hadiths in Islamic history. One of the most venerated Islamic intellectual figures, ibn Hanbal is notable for his unmatched memorization of over one million prophetic narrations, an unprecedented number that has never been claimed by any other muhaddith. Ibn Hanbal also compiled the largest hadith collection, al-Musnad, which has continued to exercise considerable influence on the field of hadith studies up to the present time, shaping the methodological framework later employed in both Sahih Bukhari and Sahih Muslim. Imam al-Dhahabi described him as “the true Imam, the proof of the religion, the master of hadith, and the leader of the Sunnah”. Imam Ali ibn al-Madini said: “Truly, Allah supported this religion through two men, to whom there is no third: Abu Bakr during the Ridda Wars, and Ahmad ibn Hanbal during the Mihna”.

Having studied jurisprudence and hadith under many teachers during his youth, Ibn Hanbal became famous in his later life for the crucial role he played in the Mihna instituted by the Abbasid caliph al-Ma'mun toward the end of his reign, in which the ruler gave official state support to the Mu'tazili doctrine of the Quran being created, a view that contradicted the orthodox position of the Quran being the eternal, uncreated word of God. Living in poverty throughout his lifetime working as a baker, and suffering physical persecution under the caliphs for his unflinching adherence to the traditional doctrine, Ibn Hanbal's fortitude in this particular event only bolstered his "resounding reputation" in the annals of Sunni history.

Abū Isḥāq Muḥammad ibn Hārūn al-Rashīd (Arabic: أبو إسحاق محمد بن هارون الرشيد; October 796 – 5 January 842), better known by his regnal name al-Muʿtaṣim biʾllāh (المعتصم بالله, lit. 'He who seeks refuge in God'), was the eighth Abbasid caliph, ruling from 833 until his death in 842. When al-Ma'mun died unexpectedly on campaign in August 833, al-Mu'tasim was thus well placed to succeed him, with the support of the powerful chief qādī, Ahmad ibn Abi Duwad, he continued to implement the rationalist Islamic doctrine of Mu'tazilism and implementing miḥna policy.

A younger son of Caliph Harun al-Rashid (r. 786–809), he rose to prominence through his formation of a private army composed predominantly of Turkic slave-soldiers (ghilmān, sing. ghulām). This proved useful to his half-brother, Caliph al-Ma'mun, who employed al-Mu'tasim and his Turkish guard to counterbalance other powerful interest groups in the state, as well as employing them in campaigns against rebels and the Byzantine Empire.

Ja'far ibn Muḥammad ibn Hārūn al-Mutawakkil ʿalā Allāh (Arabic: جعفر بن محمد بن هارون, romanized: Jaʿfar ibn Muḥammad ibn Hārūn); March 822 – 11 December 861, commonly known by his regnal name al-Mutawwakil ala Allah (Arabic: المتوكل على الله, romanized: al-Mutawakkil ʿalā Allāh, lit. 'He who relies on God'), was the tenth Abbasid caliph, ruling from 847 until his assassination in 861. He succeeded his brother, al-Wathiq (r. 842–847), and is known for expanding the empire to its maximum extent. He was deeply religious, and is remembered for discarding the Muʿtazila, ending the Mihna (a period of persecution of Islamic scholars), and releasing Ahmad ibn Hanbal. He is also known for his tough rule, especially with respect to non-Muslim subjects.

He was assassinated on 11 December 861 by the Turkic guard with the support of his son, al-Muntasir, marking the beginning of the period of civil strife known as the "Anarchy at Samarra".

Abu 'Abdallah Ahmad ibn Abi Du'ad al-Iyadi (Arabic: أبو عبد الله أحمد بن أبي دؤاد الإيادي, romanized: ʾAbū ʿAbd Allāh ʾAḥmad ibn ʾAbī Duʾād al-ʾIyādī) (776/7–June 854) was an Islamic religious judge (qadi) of the mid-ninth century. A proponent of Mu'tazilism, he was appointed as chief judge of the Abbasid Caliphate in 833, and became highly influential during the caliphates of al-Mu'tasim and al-Wathiq. During his tenure as chief judge he sought to maintain Mu'tazilism as the official ideology of the state, and he played a leading role in prosecuting the Inquisition (mihnah) to ensure compliance with Mu'tazilite doctrines among officials and scholars. In 848 Ibn Abi Du'ad suffered a stroke and transferred his position to his son Muhammad, but his family's influence declined during the caliphate of al-Mutawakkil, who gradually abandoned Mu'tazilism and put an end to the mihnah.

As one of the most senior officials during the reigns of several caliphs, Ibn Abi Du'ad's stature at the Abbasid court has been compared with that of the Barmakids at their height. Considered a leading Mu'tazilite and one of the chief architects of the mihnah, his persecution of orthodox scholars, including the famed theologian Ahmad ibn Hanbal, caused his reputation to suffer after his death, and he was made into an object of vilification by later Sunni biographers.

Abū Jaʿfar Hārūn ibn Muḥammad al-Wathiq bi'Llah (Arabic: أبو جعفر هارون بن محمد, romanized: Abū Jaʿfar Hārūn ibn Muḥammad; 18 April 812 – 10 August 847), commonly known by his regnal name al-Wathiq bi'Llah (Arabic: الواثق بالله, romanized: al-Wāthiq biʾllāh, lit. 'He who trusts in God'), was an Abbasid caliph who reigned from 842 until his death in 847.

Al-Wathiq is described in the sources as well-educated, intellectually curious, but also a poet, who enjoyed the company of poets and musicians as well as scholars. His brief reign was one of continuity with the policies of his father, al-Mu'tasim (r. 833–842), as power continued to rest in the hands of the same officials whom al-Mu'tasim had appointed. The chief events of the reign were the suppression of revolts: Bedouin rebellions occurred in Syria in 842, the Hejaz in 845, and the Yamama in 846, Armenia had to be pacified over several years, and above all, an abortive uprising took place in Baghdad itself in 846, under Ahmad ibn Nasr al-Khuza'i. The latter was linked to al-Wathiq's continued support for the doctrine of Mu'tazilism, and his reactivation of the mihna to root out opponents. In foreign affairs, the perennial conflict with the Byzantine Empire continued, and the Abbasids even scored a significant victory at Mauropotamos, but after a prisoner exchange in 845, warfare ceased for several years.