The Jewish War 5.219 (Whiston V.5.5) — William Whiston (1737), public domain (Perseus digital edition, CC BY-SA 3.0 for the digitisation) (public domain)
But the inmost part of the temple of all was of twenty cubits. This was also separated from the outer part by a veil. In this there was nothing at all. It was inaccessible and inviolable, and not to be seen by any; and was called the Holy of Holies.
Reproduced in full. Translation: William Whiston (1737), public domain (Perseus digital edition, CC BY-SA 3.0 for the digitisation) (Public domain).
Why Pitre cites it
Of the Holy of Holies in Jesus' day: 'In this there was nothing at all.' The Ark was gone.
Notes
Key phrase verbatim. One sentence of lead-in ('inmost part ... twenty cubits') kept. The Perseus URL with ':section=219' returned 'No document found'; the Whiston chapter/section form works and the same text is on Wikisource Book V ch. 5.