Albert Barnes Commentary 1 Kings 8:9

"There was nothing in the ark save the two tables of stone which Moses put there at Horeb, when Jehovah made a covenant with the children of Israel, when they came out of the land of Egypt." — 1 Kings 8:9 (ASV)

Comparing this statement with Hebrews 9:4, it would seem that Solomon, now that the sacred chest had reached its final resting place and stood in a large chamber surrounded by tables (2 Chronicles 4:8), removed the pot of manna and the rod from the interior and set them elsewhere in the Holy of Holies.