The Orb of Time is a Bajoran Orb that can send its viewer through time, used by a Klingon agent in 2373 to try to change history.
In 2373 the Klingon agent Arne Darvin, disguised as a human trader, used the Orb of Time while aboard the Defiant and took the ship and its crew back to 2268 near Deep Space Station K-7. Darvin planned to kill Captain Kirk with a bomb concealed in a tribble.
Sisko's crew found and removed the bomb without altering history. The incident brought them to the attention of the Federation's Department of Temporal Investigations.