"The Farmer and the Viper" is a fable often attributed to Aesop. Of ancient origin, it appears in several West African and European sources as well. The story concerns a farmer who finds a viper freezing in the snow. He takes pity on it and picks it up and places it within his coat. The viper, revived by the warmth, bites the farmer. The farmer cries out that he should have seen it coming.
In some versions, the farmer brings the viper home and his children go to pet it. The viper gets ready to bite the children when the farmer cuts off the viper's head.
The moral is that "kindness is wasted on evil".