Source: Guildmaster's Guide to Ravnica

Weapon (warhammer), rare (requires attunement)

You gain a +2 bonus to attack and damage rolls made with this magic weapon.

As an action, you can hurl the weapon up to 120 feet to a point you can see. When it reaches that point, the weapon vanishes in an explosion, and each creature in a 20-foot-radius sphere centered on that point must make a DC 15 Dexterity saving throw, taking 6d6 fire damage on a failed save, or half as much damage on a successful one. Afterward, you can use an action to cause the weapon to reappear in your empty hand. You can't cause it to explode again until you finish a short or long rest.

If you don't call the weapon back to your hand, it reappears at the point where it exploded when you are no longer attuned to it or when 24 hours have passed.