2 Kings 10:6-8

6And he wrote a letter the second time to them saying, If ye are mine, and will hearken to my voice, take the heads of the men your master's sons, and come to me to Jizreel to-morrow at this time. Now the king's sons, seventy persons, were with the great men of the city, who brought them up.

7And it came to pass when the letter came to them, that they took the king's sons, and slaughtered seventy persons, and put their heads in baskets, and sent them to him to Jizreel.

8And a messenger came and told him saying, They have brought the heads of the king's sons. And he said, Lay them in two heaps at the entrance of the gate until the morning.