2 Kings 10:6-7

6Then Jehu wrote them a second letter, saying: If you are on my side, and if you will obey me, bring me the heads of your master’s sons at this time tomorrow at Jezreel. All seventy of the king’s sons were being cared for by the city’s prominent men.

7When the letter came to them, they took the king’s sons and slaughtered all seventy, put their heads in baskets, and sent them to Jehu at Jezreel.