From Zelda Wiki, the Zelda encyclopedia
Stone Slabs and Stone Slab Fragments are items found only in the original version of Link's Awakening.
Stone Slabs are tablets that can be found hanging in each of the eight dungeons on Koholint Island. Each Slab holds a message, but cannot be read because a part of it is missing. Link must explore the dungeon until he finds a Treasure Chest containing the missing fragment. He can then return the fragment to the slab, revealing a clue about a puzzle, a monster, or a dungeon boss or mini-boss.