Bava Metzia 86 - The Story of Rabbah Bar Nachmani
Slanderers told the king that there was a man among the Jews who made twelve thousand of them idle for two months a year by teaching them Torah, and Rabbah had to flee.
Finally he escaped to a marsh and was studying there. In the Heavenly Academy there was an argument about impurity connected to skin discolorations . If a white hair grew on a white spot, it was impure. If a white spot appeared under a white hair, it was pure. What if it was not known which came first? God was saying it is pure, and the Academy ruled that it is impure. They called Rabbah to decide on the issue, and his soul ascended to heaven.