Exodus 28:27-28

27You are to make two gold rings and attach them to the lower part of the two shoulder pieces of the ephod in front, close to the place where it is joined, above the skillfully woven sash of the ephod.

28They shall bind the breastpiece by its rings to the rings of the ephod with a blue cord, so that it will be above the skillfully woven sash of the ephod, so that the breastpiece will not come loose from the ephod.