Yahweh prepared a great fish to swallow up Jonah, and Jonah was in the belly of the fish three days and three nights.
"Three days and three nights ..." Most commentators move quickly to protect the popular superstition regarding this being a reference to the so-called "Hebrew idiom," in which any part of three days and three nights, as for example two partial days, one whole day, and two nights may properly be called "three days and three nights!"  However, we reject this, not only as it is alleged to apply here to the experience of Jonah, but in the fact of its application to the experience of Christ as well, who was in the grave "three days and three nights," rising the third day.  Sunday was described in the Book of Luke as "The third day since" the crucifixion (Luke 24:21); and there is no honest way to make that mean that Sunday is the third day since Friday!  (See my dissertation on this entire subject in my commentary on Mark, pp. 343-351.)