This melody is said (in Chassidic circles...we all find ourselves in one of those all the time I know) to have been "bought" by Rabbi Schneur Zalman from a Russian shepherd whom he heard singing it. Recognizing that it was a melody sung in the Holy Temple, Rabbi Schneur Zalman asked the shepherd if he could "buy" it. The shepherd laughed and coyly agreed. The rabbi asked him to sing it and teach it to him. He obliged. After which the shepherd couldn't remember the tune again. About Chassidic stories they say, "If you believe them all you're a fool....