Rabbi said: When Saul came to the camp of Amalek he saw the children of Israel tarrying in the midst of Amalek. He said to them: Separate yourselves from the midst of Amalek, as it is said, "And Saul said unto the Kenites, Go, depart, get you down from among the Amalekites, lest I destroy you with them" (1 Sam. 15:6). Did Jethro show loving-kindness to all Israel? But did he not show loving-kindness to Moses our teacher alone? Hence thou mayest learn || that whosoever shows loving-kindness unto one of the great men of Israel is considered as though he had shown loving-kindness unto Israel. Because of the loving-kindness which he showed, his children were saved from among the Amalekites.
Saul in Battle of Amalekites
Pirkei DeRabbi Eliezer 44:11