II Samuel 13:28

"Now Absalom had commanded his servants, saying, 'Watch now, when Amnon's heart is merry with wine, and when I say to you, "Strike Amnon!" then kill him. Do not be afraid. Have I not commanded you? Be courageous and valiant.'"

(It's easy for sibling squabbles to turn into something far worse. Amnon committed the sin of incest, but Absalom nudged him on to do so. Nevertheless, he hated Amnon for doing it. Siblings are your siblings as long as you live. Don't treat them like they're your enemies.)