The Book of Elchasai or the Book of Elxai is a lost prophetic book, written during the reign of Trajan (reigned 98 –117), that contained laws and apocalyptic prophecies pertaining to Jewish Christian and Gnostic doctrines. It is known only from fragments quoted in the early Christian writings of Hippolytus of Rome, Eusebius, Epiphanius of Salamis, and Origen. The book was used by a number of Transjordanian sects, including Ebionites, Essenes, Nazarenes, and especially by Elcesaites whom based their origins from.