Ibn Ezra on Leviticus 16:4

כתנת בד קדש. ולא הזכיר האפוד והחשן ומעיל האפוד כי כבר הזכיר ונשמע קולו בבואו אל הקדש ומזה הכתוב למדו אנשי בית שני ששמשו בלא אורים ותומים גם נביאים היו שם: THE HOLY LINEN TUNIC. Scripture does not mention the ephod,¹⁸See Ex. 28:6-12. the breastplate,¹⁹Ex. 28:15-27. and the robe of the ephod,²⁰Ex. 28: 31-35. for it earlier mentioned, and the sound thereof²¹The sound of the bells of the ephod. shall be heard when he²²The kohen gadol. goeth in unto the holy place (Ex. 28:35).²³The point is Ex. 28:35 tells us that the kohen must wear the robe when he enters the Holy of Holies. Now, the ephod and the breastplate were attached to the robe. Hence there was no need for Scripture to repeat once again that Aaron shall wear these garments when he enters the Holy of Holies. Rashbam on Ex. 28:35 explains similarly. It should be noted that this interpretation is contrary to the accepted halakhic opinion which rules that the kohen gadol does not enter the Holy of Holies wearing the ephod, its band, the breastplate, and the robe. See Rosh Ha-Shanah 26a. Also see Rashi, “This teaches us that he must not officiate in the interior (the Holy of Holies) robed in the eight garments which were the insignia of the High Priest…in which he performed the service outside…but in the four garments…like an ordinary priest” (Rosenbaum and Silbermann). The men of the second temple who served without the Urim and the Thummim²⁴Which was placed in the breastplate (Ex. 28:30). learned from this verse [that their practice was proper].²⁵Since Scripture does not mention the Urim and the Thummim in our verse, it appears that the wearing of the Urim and the Thummim is not essential for the service to be valid. There were also prophets there.²⁶At the beginning of the second temple period. These prophets taught the Israelites that the kohen gadol may officiate without the Urim and the Thumim if the latter are not available.