jump to conclusions = leap to conclusions = jump the conclusion that = leap to the conclusion that
make a hasty judgement or decision before learning or considering all the facts.
Related Idioms :
try conclusions with
engage in a trial of skill or argument with
1902 - G. S. Whitmore - The Last Maori War in New Zealand - Te Kooti's prestige enormously increased by an apparent unwillingness to try conclusions with him, even with an immensely superior force and in the open plains.