Go into the WIND TEMPLE and you are outside the boss room, break the jar on the left side closest to the boss door and a bunch of different colored rupees will fly out. Pick them up and jump into the magic cauldron and teleport to the first jar you uncovered. Jump in the one you just popped out of and keep doing that until you get back to the boss door. Then break the jar again and all the rupees will be there again. Repeat the process as many times as you like!