Putin was referencing a quote by Denikin. It was about how the Ukraine crisis is only relevant to Russia and Ukraine themselves.Where can I read more about this? I remember watching a Putin speech where he mentioned Denikin, and so I'm interested
The good sources are books. Actually, Denikin himself wrote multiple books on the Civil War.
The wikipedia page on Denikin contains the most online information, and the Russian language version is better.
This website contains some journal entries by him.