Albert Barnes Commentary 2 Samuel 19:24

"And Mephibosheth the son of Saul came down to meet the king; and he had neither dressed his feet, nor trimmed his beard, nor washed his clothes, from the day the king departed until the day he came home in peace." — 2 Samuel 19:24 (ASV)

Beard - The “moustache,” the beard of the upper lip. The fact related in this verse tends to clear Mephibosheth from the suspicion of unfaithfulness to David.