Aḥmad b. ʿĪsā (3rd/9th century), one of the earliest experts in optics ( ʿilm al-manāẓir) in the Islamic world. Nothing is known of his life, and his al-Manāẓir wa al-marāyā al-muḥriqa (‘Optics and Burning Mirrors’) is the only work of his to have survived. In this book, Aḥmad b. ʿĪsā first examines the eye and how it works. He argues that a luminous power ( quwwa nūriyya) emanates from the eye, producing a cone of light, the apex of which is in the eye and the base lies at the visible object. He then describes the structure of the eye, how rays of light from …

Aḥmad b. ʿĪsā b. Zayd, Abū ʿAbd Allāh (c. 157–247/773–861), grandson of Zayd b. ʿAlī b. Ḥusayn b. ʿAlī b. Abī Ṭālib, was one of the well-known ʿAlids during the early ʿAbbāsid caliphate and a prominent Zaydī scholar. He became known as al-mukhtafī (‘the hidden one’) because he lived in hiding for a period. The sources are at variance over the details of his life. His mother was ʿĀtika, daughter of Faḍl b. ʿAbd al-Raḥmān b. al-ʿAbbās b. Rabīʿa b. al-Ḥārith b. ʿAbd al-Muṭṭalib (al-Bukhārī, 65). According to al-Bukhārī (p. 66), he was born in 158/775 …

Akhbāriyya, adherents of a school of thought in late Imāmī law ( fiqh) who favour ḥadīth (traditions) and akhbār (reports) over uṣūl al-fiqh (principles of jurisprudence). In contrast to them are the jurists who follow ijtihād (independent legal reasoning) and are known as Uṣūlīs. Quite apart from the technical terms akhbārī and uṣūlī, the contrasting attitudes to which these terms refer have their roots in the early centuries of Shiʿi jurisprudence, when there were factions who practised ijtihād and others who followed tradition. During the 4th/10th century the traditionalist…

Aḥdāth, plural of ḥadath, is a term with several different meanings: young men, temporal events, calamities and innovations. In the history of Islam it has taken on a range of technical meanings, although how some of these applied in particular circumstances is not entirely clear. The historical sources indicate that the term appears to have been introduced during the time of the second caliph, ʿUmar, when a position was created with the title of commander or amīr of the aḥdāth. The holder of the post was required to investigate affairs that were deemed to be innovations o…

Aḥmad Kāsānī, son of Jalāl al-Dīn (866–949/1461–1542), was one of the great spiritual masters of the Khwājagān-Naqshbandiyya order in Transoxiana in the 9th–10th/15th–16th century. His laqabs were Khwājagī Aḥmad and Makhdūm Aʿẓam, and he was also known as Dahbīdī because of the place where he was buried (Samarqandī, 179; Chishtī, 1/319, 322; Rashād, 76). Born in 866/1461, he came from Kāsān, a town situated to the north of the Jaxartes (Syr Daryā) in the Farghāna valley (Yāqūt, 4/227; Rashād, 73). Kāsānī is said to have traced his ancestry through …