Boris hasn’t claimed he didn’t say that yet, however some sources I found:

https://www.tradingview.com/news/benzinga:812300914094b:0-tucker-carlson-claims-boris-johnson-quoted-1m-in-us-dollars-gold-or-bitcoin-for-an-interview-about-ukraine/

https://tass.com/world/1749469

https://youtu.be/CVzE0RB_DKo

https://www.republicworld.com/world-news/boris-johnson-demanded-1-million-for-interview-says-tucker-carlson-after-putin-sit-down/

https://www.spectator.co.uk/article/tucker-carlsons-spat-with-boris-johnson-turns-nasty/

There’s probably more sources that say this