Jamieson, Fausset and Brown on 1 Samuel 31:3-5

3-5. the battle went sore against Saul, &c.--He seems to have bravely maintained his ground for some time longer; but exhausted with fatigue and loss of blood, and dreading that if he fell alive into the enemy's hands, they would insolently maltreat him (Jos 8:29; 10:24; Jud 8:21), he requested his armor bearer to despatch him. However, that officer refused to do so. Saul then falling on the point of his sword killed himself; and the armor bearer, who, according to Jewish writers, was Doeg, following the example of his master, put an end to his life also. They died by one and the same sword--the very weapon with which they had massacred the Lord's servants at Nob.