After Sahasrahla gives Link the Pegasus Shoes, he tells him to get a strange and mystical weapon called the Ice Rod which is located to the east of Lake Hylia. Link must travel south of the lake and then up and around to the lake's northeast corner. Link will be able to see a cave entrance, but just to the left of that entrance is a pile of loose rocks. Bomb through the rocks to reveal another entrance."
"An icy blast flies out from the Ice Rod. It freezes enemies solid."
"Once frozen, Link can pick up an enemy and throw it to destroy it."
Despite Link being able to acquire the Ice Rod before even entering the Eastern Palace, the item isn't required until near the very end of the game. Link will need the Ice Rod in Turtle Rock when battling against the dungeon boss, Trinexx.