Effect 77-78 of the wild magic surge table in the Player's Handbook states:
You cast polymorph on yourself. If you fail the saving throw, you turn into a sheep for the spell's duration.
Polymorph's spell description then says:
The target's game statistics, including mental ability scores, are replaced by the statistics of the chosen beast.
However, I'm unable to find the game statistics of a sheep, either in the Monster Manual or Appendix D of the Player's Handbook itself. Did I overlook something? Is there an official source of this creature's statistics?