1 Samuel 17:12-15

Now David was the son of the Ephrathite of Bethlehem in Judah, named Jesse, who had eight sons. Jesse was old in the days of Saul, advanced in years among men. His three older sons had followed Saul into battle. The names of his three sons who went to battle were Eliab, the firstborn; next, Abinadab; and third, Shammah. David was the youngest. Now the three oldest followed Saul, but David went back and forth from Saul to tend his father’s flock at Bethlehem.