PHB, page 230

Delayed Blast Fireball

7-level Evocation

A beam of yellow light flashes from your pointing finger, then condenses to linger at a chosen point within range as a glowing bead for the duration. When the spell ends, either because your concentration is broken or because you decide to end it, the bead blossoms with a low roar into an explosion of flame that spreads around corners. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A creature takes fire damage equal to the total accumulated damage on a failed save, or half as much damage on a successful one.

  The spell's base damage is 12d6 . If at the end of your turn the bead has not yet detonated, the damage increases by 1d6 .

  If the glowing bead is touched before the interval has expired, the creature touching it must make a Dexterity saving throw. On a failed save, the spell ends immediately, causing the bead to erupt in flame. On a successful save, the creature can throw the bead up to 40 feet. When it strikes a creature or a solid object, the spell ends, and the bead explodes.

  The fire damages objects in the area and ignites flammable objects that aren't being worn or carried.

At higher levels: When you cast this spell using a spell slot of 8th level or higher, the base damage increases by 1d6 for each slot level above 7th.