Exodus 28:28

28:28 They are to tie the breastpiece by its rings to the rings of the ephod by blue cord, so that it may be above the waistband of the ephod, and so that the breastpiece will not be loose from the ephod.

Exodus 39:21

39:21 They tied the breastpiece by its rings to the rings of the ephod by blue cord, so that it was above the waistband of the ephod, so that the breastpiece would not be loose from the ephod, just as the Lord had commanded Moses.