Exodus 28:35-37

35And it shall be upon Aaron when he ministers, and its sound will be heard when he goes into the holy place before the Lord and when he comes out, that he may not die.

36“You shall also make a plate of pure gold and engrave on it, like the engraving of a signet: HOLINESS TO THE LORD.

37And you shall put it on a blue cord, that it may be on the turban; it shall be on the front of the turban.