And there fell some of Manasseh to David, when he came with the Philistines against Saul to battle: but they helped them not: for the lords of the Philistines upon advisement sent him away, saying, He will fall to his master Saul to the jeopardy of our heads. (1 Chronicles 12:19)
This was on the occasion of Saul’s last battle (1 Sam. 29:1-11), when David accompanied the Philistines to the battle, but was dismissed before the outbreak of hostilities.