His epitaph, written by himself (translation): Man will not always stay on Earth; the pursuit of light and space will lead him to penetrate the bounds of the atmosphere, timidly at first, but in the end to conquer the whole of solar space.

Mentioned in Beyond the Planet Earth, by K. Tsiolkovsky (1920), translated by K. Syers (1960), reviewed by M. G. Whillans, Journal of the Royal Astronomical Society of Canada, Vol. 55 (1961), p. 144

https://articles.adsabs.harvard.edu/full/seri/JRAS...[articles.adsabs.harvard.edu]