Rashi on Genesis 43:31/רש"י על בראשית מ״ג:ל״א

1ויתאפק AND HE REFRAINED HIMSELF — He made a strong effort. The root in this sense occurs in (Job 41:7) אפיקי “the strong parts of the shields”. Similar also is (Job 12:21) “And He looseth the belt of the (אפיקים) strong”.