Then Jehu wrote them a second letter, saying, "If you are on my side and will obey me, take the heads of your master's sons and come to me in Jezreel by this time tomorrow." Now the royal princes, seventy of them, were with the leading men of the city, who were rearing them.
When the letter arrived, these men took the princes and slaughtered all seventy1 of them. They put their heads2 in baskets and sent them to Jehu in Jezreel.
References for 2 Kings 10:7
When the messenger arrived, he told Jehu, "They have brought the heads of the princes." Then Jehu ordered, "Put them in two piles at the entrance of the city gate until morning."
The next morning Jehu went out. He stood before all the people and said, "You are innocent. It was I who conspired against my master and killed him, but who killed all these?
Know then, that not a word the LORD has spoken against the house of Ahab will fail. The LORD has done what he promised3 through his servant Elijah."4
References for 2 Kings 10:10