He's referring to a verse in Ezekiel. The passage reads:
The word of the Lord came again unto me, saying, Moreover, thou son of man, take thee one stick, and write upon it, For Judah, and for the children of Israel his companions: Then take another stick, and write upon it, For Joseph, the stick of Ephraim, and for all the house of Israel his companions: And join them one to another into one stick; and they shall become one in thine hand. (Ez 37:15-17, KJV)
This is one of several passages Mormons try to conscript to prove the Bible spoke of another inspired work of scripture that was to be brought forth in the "latter days."
Mormons rely greatly on the Ezekiel passage as a proof text to demonstrate not only the possibility of divine scripture aside from the Bible, but also the Book of Mormon's doctrinal equality with it. They assume that the "stick of Judah" is the Bible, while the "stick of Joseph" is the Book of Mormon. In these, the latter days, the two have been joined together, forming the bulk of Mormon scripture.
Mormonism's professed literal interpretation of Scripture does not extend to hundreds of passages it rejects as corrupted or that it skews to suit its own purposes. In the case of Ezekiel 37, Mormons not only neglect the plain sense of the words but also ignore their true interpretation, given by God--in the very same chapter.
First, the Hebrew term translated as "stick" (aits) is never used anywhere in the Old Testament to mean "book," "scroll," "writing" or anything similar. It is variously translated as "wood" or "branch," "timber," or "tree." Needless to say, the Book of Mormon was allegedly written on metal plates, not scrolls or sticks.
Second, the correct interpretation of this symbolic action of the prophet is given just a few verses later. Ezekiel is to take the two sticks, put them end to end and hold the joined ends in his hand. He thus displays to the people a "single" stick, once again united. This is to show that the scattered remnants of the Southern kingdom ("Judah") and Northern kingdom of Israel ("Joseph") will be returned from exile, restored to their land, and made one nation again. "They shall be no more two nations, neither shall they be divided into two kingdoms any more at all" (Ez 37:22).
With divine impetus, Ezekiel first spoke this parable of redemption then enacted it. Only Mormonism can manage to mistake "timber" for "scrolls" and "nations" for "metal plates."
Take a look at the passage in a more modern translation:
The word of the Lord came to me: "Son of man, take a stick and write on it, 'For Judah, and the children of Israel associated with him,' then take another stick and write upon it, 'For Joseph (the stick of Ephraim) and all the house of Israel associated with him,' and join them together into one stick. . . . Behold, I am about to take the stick of Joseph (which is in the hand of Ephraim) and the tribes of Israel associated with him; and I will join with it the stick of Judah, and make them one stick, that they may be one in my hand. . . . I will take the people of Israel from the nations among which they have gone, and will gather them from all sides, and bring them to their own land; and I will make them one nation in the land, upon the mountains of Israel; and one king shall be king over them all; and they shall be no longer two nations, and no longer divided into two kingdoms." (Ez 37:15-22, RSV)
As the text makes clear, this is a prophecy of national reunification, not about the appearance of hidden scriptures.