When Rabbi Eliezer ben Hyrcanus, called the Great, lay dying, he gathered his students for a last round of teachings that has the quality of prophecy more than of instruction.
He looked each disciple in the eye and foretold the manner of his death. He told some that they would die of sword, others of fire, others of peaceful old age. He foretold most precisely the martyrdom of Rabbi Akiva, whose flesh would be combed with iron rakes by the Romans and whose final word would be the Shema, drawn out on the last breath.
Akiva himself asked the dying master about the scope of what he had been taught. Rabbi Eliezer used the image that would echo through Jewish literature forever: "If all the seas were ink, and all the reeds were pens, and all the sky were parchment, and every human being were a scribe, they still could not write down all that I received from my teachers." He was not boasting. He was testifying to the tradition's vastness compared to any single lifetime's ability to record it.
He taught Akiva, on that final day, a discipline so subtle the Talmud keeps it almost as a secret. By speech alone, Rabbi Eliezer could cause gourds to sprout in a field. By speech alone, he could make them vanish back into the soil. He demonstrated the practice for Akiva's memory, not to impress him, but so that the chain would not break.
Then he fell silent. When he opened his mouth one last time, he pronounced a single word, and that word was tahor, "clean." His soul departed on the syllable. In an argument about purity that had dogged his life, his last breath declared the verdict (Gaster, Exempla No. 126).
A teacher, the sages say, should leave the world the way Rabbi Eliezer left it: still teaching, still answering the question he had lived his life to answer.