Leviticus Rabbah 6.2

There once was a governor who used to put to death receivers of stolen property and release the thieves, and all used to find fault with him, saying that he was not acting correctly. What did he do? He issued a proclamation throughout the province, saying: 'Let all the people go out to the public field!" What did he do then? He brought some weasels and placed before them portions of food. The weasels took the portions, and carried them to their holes. The next day he again issued a proclamation, saying: "Let all the people go out to the public field!" Again he brought weasels and placed portions of food before them but this time he stopped up all the holes. The weasels took the portions, and carried them to their holes, but finding these stopped up, they brought their portions back to their places. [He did this] to demonstrate that all the trouble is due to receivers. [Soncino Translation]