What did God tell Hosea to name his first son?

Answer: Jezreel

The firstborn was named Jezreel, for God would bring the bloodshed of Jezreel upon the house of Jehu.

“So Hosea went and married Gomer daughter of Diblaim, and she conceived and bore him a son. Then the LORD said to Hosea, “Name him Jezreel, for soon I will bring the bloodshed of Jezreel upon the house of Jehu, and I will put an end to the kingdom of Israel.”— Hosea 1:3-4 (BSB)