וְיִרְכְּס֣וּ אֶת־הַ֠חֹשֶׁן מטבעתו [מִֽטַּבְּעֹתָ֞יו] אֶל־טַבְּעֹ֤ת הָאֵפֹד֙ בִּפְתִ֣יל תְּכֵ֔לֶת לִֽהְי֖וֹת עַל־חֵ֣שֶׁב הָאֵפ֑וֹד וְלֹֽא־יִזַּ֣ח הַחֹ֔שֶׁן מֵעַ֖ל הָאֵפֽוֹד׃
On assujettira le pectoral en joignant ses anneaux à ceux de l’éphod par un cordon d’azur, de sorte qu’il reste fixé sur la ceinture de l’éphod; et ainsi le pectoral n’y vacillera point.
Sefer HaMitzvot
He prohibited us from removing the breastplate from the ephod (a type of apron worn by the high priest), but rather that the breastplate be attached to it. And at the end of Makkot (Makkot 22a), they said when they mentioned those liable for lashes, "But behold, there is [also] the one who loosens the breastplate!" Behold it is already been made clear that one who loosens [it] is lashed. (See Parashat Vayakhel; Mishneh Torah, Vessels of the Sanctuary and Those who Serve Therein 9.)