How do I know?
In 2 Chronicles 1 we can read about Solomon making offerings at Gibeon where the old tabernacle of Moses was pitched. The bronze altar was still there, but the most important item, the Ark of the Covenant had already been moved by David to a special spot in the City of David.
The record says (v.4) ‘David had brought up the ark of God from Kirjath-Jearim to the place David had prepared for it, for he had pitched a tent for it in Jerusalem.’
We know where that tent was, for when Solomon had been anointed for kingship, David had instructed Nathan the prophet and Zadok the priest and Benaiah the son of Jehoiada to put Solomon on the royal mule and taken to Gihon (see 1 Kings 1:32ff) and note that v.39 informs us that Zadok took the horn of oil ‘from the tent and anointed Solomon.’
Note, it’s called in 2 Chronicles 1:4 (above) ‘the place David had prepared for it.’
And…where did Solomon start building the temple? At that very place: for the same words are used in 2 Chronicles 3:1--
‘Now Solomon began to build the house of the LORD at Jerusalem on Mount Moriah, where the LORD had appeared to his father David, at the place that David had prepared …’
Indeed, in my view, the tent was at Gihon, at the site known through the ages as HaMakom (The Place)—and further, that the threshing floor had been there on one of the ledges just above the floor of Kidron Valley and just near the Spring Gihon. In fact, having stood in all these places, I know well how the Kidron Valley is a funnel for the breezes, which in Jerusalem prevail from WNW to WSW! The picture is an artist's impression of the City of David with the fortress wall extending East around Gihon Spring.
Remember that when the text says, ‘on mount Moriah’ it is referring to the whole of that mountain, of which the southern ridge on which the City of David was built, forms part.