Mishnah Chagigah on Abandoning the Torah

"'Who is 'a crooked one who cannot be straightened' (Ecclesiastes 1:15)? Rabbi Shim'on ben Yochai says: We do not refer to someone as 'crooked' unless he was straight at first and then became crooked. And who is this? This is a Torah scholar who abandons the Torah."

-- Mishnah, Chagigah 1:7