Jonah 1.17
Septuagint

kai 
hn IwnaV en th koilia tou khtouV 
treiV hmeraV kai treiV nuktaV

New Testament - Matthew 12.40

wster gar 
hn IwnaV en th koilia tou khtouV 
treiV hmeraV kai treiV nuktaV

Septuagint

and Jonas was in the belly of the whale three days and three nights

New Testament

for as Jonah was three days and three nights in the belly of the whale

Masoretic Text

and Jonah was in the belly of the fish three days and three nights

Comments:  The NT and the LXX agree.  As the Greek word khtoj can also mean a gigantic fish, the MT is not significantly different.