どんなことがあっても決(けっ)して口(くち)をきかないこと。

When Toshishun became poor again and was sitting on the road, the same old man appeared again. The old man gave him a large sum of money for the second time, but Toshishun spent it all in the same way. The third time was also a repeat of the same. The old man said, "You really don't seem to know how to use money. Why don't you become my disciple? However, no matter what happens, you must never speak. If you utter even a single word, you will not be able to return to the human world."