Litta Jātaka (No.91)
The Bodhisatta was once a dice player, and used to play with a sharper who, when he saw that he was losing, would put one of the dice in his mouth, pretending that it was lost. The Bodhisatta discovered this, and one day brought dice smeared with dried poison. The sharper played his usual tricks, and suffered great pain from the poison. The Bodhisatta then cured him, thus teaching him to be honest in future. The story was told in reference to certain monks who were careless in the use of various requisites given to them. J.i.379 f.