John Gill Commentary 1 Samuel 26:18

"And he said, Wherefore doth my lord pursue after his servant? for what have I done? or what evil is in my hand?" — 1 Samuel 26:18 (ASV)

And he said, wherefore does my lord thus pursue after his
servant ?
&c.] Suggesting that it was both below him to do it, and against his interest; for David was his servant, and he would gladly have continued in his service, and done his business, but he drove him from it, and pursued him as a traitor, when he had not been guilty of any offence to his knowledge: and therefore puts the following questions:

for what have I done? or what evil [is] in my hand ?
what crime had he committed, that he was pursued after this manner, and his life sought for? what had he done worthy of death? having a clear conscience, he could boldly ask these questions.