Jehoshaphat (also spelled Jehosophat and Jehosaphat) was an exclamation frequently uttered by the Third Doctor, sometimes prefixed with "jumping".
In Russia in 1916, the Third Doctor exclaimed "Jumping Jehoshaphat!" when he saw that Vladimir Purishkevich and Ivan Sukhotin had thrown Grigori Rasputin into the Neva River. (PROSE: The Wages of Sin)
On Dust, the Third Doctor muttered "Jehoshaphat" when he realised that his first incarnation had been brought to 76 Totter's Lane because it was actually I.M. Foreman's Travelling Show. (PROSE: Interference - Book Two)
In Mesopotamia, the Seventh Doctor summoned his third incarnation's personality to defuse Ishtar's cobalt bomb. The Doctor exclaimed "Jumping Jehoshaphat!" upon seeing how his seventh self was dressed. He said it again when he found that Ishtar was no longer in the TARDIS' telepathic circuits. (PROSE: Timewyrm: Genesys)