Amasa was a man's son, whose name was Ishra an Israelite. 2 Samuel 17:25
And the father of Amasa was Jether the Ishmaelite. 1 Chronicles 2:17
Note from The Harper Collins Study Bible for 2 Samuel 17:25: "The information about Amasa's parentage is textually uncertain; evidently he was the child of an Ishmaelite, ...."