The princes refrained talking - As a mark of respect, or in awe of his presence.
And laid their hand on their mouth - To lay the finger or the hand on the mouth is every where an action expressive of silence or respect; Notes, Job 21:5. "In one of the subterranean vaults of Egypt, where the mummies lie buried, they found in the coffin an embalmed body of a woman, before which was placed a figure of wood, representing a youth on his knees, laying a finger on his mouth, and holding in his other hand a sort of chafing dish, which was placed on his head, and in which, without doubt, had been some perfumes." Maillet.

The princes refrained talking - They never ventured an opinion in opposition to mine; so fully were they persuaded of the justice and integrity of my decision.

The princes refrained talking, and laid [their] hand on their (f) mouth.
(f) Acknowledging my wisdom.

The princes refrained talking,.... Who were in court before Job came in, and were either talking with one another about indifferent matters, or were giving their opinion in a case before them; but no sooner did Job make his appearance, but they left off talking, and would not proceed any further; they laid a restraint upon their words, and curbed themselves from speaking any more till they had heard his opinion:
and laid their hand on their mouth; as a token of silence, Judges 18:19.

(Job 4:2; see on Job 21:5).
Refrained talking--stopped in the middle of their speech.