A man in Pumbedita offended Rav Yehuda. The man used to call other people slaves. Rav Yehuda excommunicated him and pronounced him a slave. In the court of Rav Nachman, Rav Yehudah explained that he pronounced the man slave because he called others slaves. Usually, this only allows one to suspect, but on that day, Rav Matna, who had not visited Pumbedita for 13 years, came and confirmed that the man was a slave, and more blemishes were discovered.
Art: Karoly Ferenczy - Joseph Sold Into Slavery By His Brothers