Exodus 28:36-39

28:36 “You are to make a plate of pure gold and engrave on it the way a seal is engraved: “Holiness to the Lord.” 28:37 You are to attach to it a blue cord so that it will be on the turban; it is to be on the front of the turban, 28:38 It will be on Aaron’s forehead, and Aaron will bear the iniquity of the holy things, which the Israelites are to sanctify by all their holy gifts; it will always be on his forehead, for their acceptance before the Lord. 28:39 You are to weave the tunic of fine linen and make the turban of fine linen, and make the sash the work of an embroiderer.

Leviticus 8:9

8:9 Finally, he set the turban on his head and attached the gold plate, the holy diadem, to the front of the turban just as the Lord had commanded Moses.