As recorded in [I *Sh'muel* (chapter 15)](http://he.wikisource.org/wiki/%D7%A9%D7%9E%D7%95%D7%90%D7%9C_%D7%90_%D7%98%D7%95), *Shaul*, the king, was told by the prophet to destroy the nation of *Amalek*

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> from man to woman, youngster to suckling, ox to sheep, camel to donkey.
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So he gathered an army, and killed out *Amalek*, except for some animals and the king, *Agag*. Why didn't he kill *Agag*?