The book of Jasher (or the Book of the Upright) is a work referenced in the Old Testament, but now lost.
It appears to be the original source of the miracle described in Joshua 10:13, where God makes the sun stand still so Joshua can finish killing his enemies.
At least two manuscripts claiming to be the Book of Jasher have surfaced. One was a forgery published in English in 1751, and since reprinted by the Rosicrucians. The other was a translation of a medieval Hebrew text incorporating and expanding on content from Genesis and other Old Testament books. It was translated into English and published in 1840, and gained some popularity among early Mormons when Joseph Smith wrote favorably of it. Academics and Bible scholars reject the first version as an obvious forgery, and the second version as being of no earlier than medieval origin, and therefore more than 2000 years too late.