Muḥammad ibn Jaʻfar al-Izkiwī was a leading Muslim scholar who lived in about 900. His name, al-Izkiwī, suggests that he came from Izkī, one of the oldest cities and centers of learning in the interior of Oman. Jāmiʻ al-adyān (The compendium of faith), sometimes referred to simply as al-Jāmiʻ (The compendium) or Jāmiʻ Ibn Jaʻfar (Ibn Jaʻfar’s compendium), is his best-known work. Shown here is an 18th-century manuscript containing the first part of Jāmiʻ al-adyān. As the title suggests, the book summarizes a wide range of topics in Islamic jurisprudence from an Ibadite (also seen as Ibadhite and Ibadi) perspective. Ibadism is an Islamic denomination that traces its roots to the seventh century, at the time of the Sunni−Shiite schism. It is named after Abdullāh ibn Ibāḍ, one of the founding scholars of the doctrine. Today’s adherents of Ibadism are found primarily in Oman, in addition to other communities in North and East Africa. This work discusses topics pertaining to the five pillars of Islam, including the five daily prayers, the fasting at Ramadan, and almsgiving. It includes many edicts that are related to these topics. The manuscript, in a good condition despite some water damage on the margins, was paid for by a bequest of Sheikh ʿUmar ibn Saʿīd al-Bahlawī. It was copied by Saʿīd ibn Muḥammad ibn ʿUdai al-ʿAbrī in 1156 AH (1743). In addition to catchwords, the margins include corrections, elaborations, and paraphrasing of the main text. The book is divided into more than 80 bāb (chapters), which are in turn divided into opinions and masāʼil (issues). Interesting additions include a listing of the currencies used in Oman at the time.