1 Kings 16:15-17

15When Asa had been king of Judah for 27 years, Zimri became king of Israel. He ruled as king in Tirzah for seven days. When Zimri killed King Elah, Israel's army was attacking a Philistine town called Gibbethon.

16The army received this message: ‘Zimri has turned against the king and he has killed King Elah.’ Omri was the officer who led Israel's army. That day, Omri's soldiers decided to make Omri the king of Israel, while they were in their camp at Gibbethon.

17So Omri and all Israel's army left Gibbethon and they went to attack Tirzah.