The three older sons of Jesse had followed Saul into battle: The firstborn was Eliab, the second was Abinadab, and the third was Shammah.
Jewish Publication Society of America Version (JPS1917) - 1 Samuel 17:13 >And the three eldest sons of Jesse had gone after Saul to the battle; and the names of his three sons that went to the battle were Eliab the first-born, and next unto him Abinadab, and the third Shammah.