The “prophet that teacheth lies” is named in Nephi’s quotation of Isaiah (2 Nephi 19:15), where the Lord declares he will cut off from Israel “head and tail, branch and rush in one day” (2 Nephi 19:14). Within that figure the ancient, or elder, is the head, and the prophet that teacheth lies is the tail (2 Nephi 19:15).
The oracle is directed at Ephraim and the inhabitants of Samaria, who spoke in the pride of their hearts that they would rebuild greater after destruction (2 Nephi 19:9-10). The leaders of the people cause them to err, and those led by them are destroyed (2 Nephi 19:16).