Komentarz do Diwrej ha-jamim I 15:26

And it came to pass when God helped the Levites - Heb. בֶּעְֹזר. The “beth” of בֶּעְֹזר is vowelized with a “segol,” but as a rule, it is vowelized with a “pattah.” The meaning of “when [God] helped,” is that they did not err when they carried the Ark as they had erred in the beginning when Uzza died. And in the Book of Samuel (II 6:13), it says that when they had trodden six paces, they made this sacrifice. Our Rabbis derived from here that the Ark carried itself.