The Books of Djehuti are texts used in the Trial of Ra. The texts contains all the knowledge of Ra's true history and language, along with the password and address of the Stargate via an implant. When the trial ended, the participant must choose whether to retain the knowledge of Ra's true history or his language.
In 1999, when SG-1 was forced to attempt the trial of Ra and during the test the Books of Djehuti downloaded their knowledge and Ra's true language into Teal'c. When the trial was completed Teal'c chose to keep the knowledge reasoning that Daniel Jackson would one day be able to translate the language. His symbiote was kept stationary until the implant was removed. (SG1: "The Barque of Heaven")