Not everyone would be willing to say that he believes in the existence of the neutrino, but it is safe to say there is hardly one of us who is not served by the neutrino hypothesis as an aid in thinking about beta-decay process.
The Energy and Momentum Relations in the Beta-Decay and the Search, for the Neutrino, Review of Modern Physics, Volume 20, Number 2, March, 1948 (p. 278)
