He ran away.
3 seconds sound clip from the Mister Ed - Season 1, Ep. 4 - Kiddy park TV Series.
You can hear this line at 00:19:59 in the DVD version of the movie.
Quote context
[...]
- Children. Where do they get those imaginations?
- Wilbur!
- Carol!
- What's Mister Ed doing here?
- Don't tell me he wanted to visit his relatives on the merry-go-round.
- By the time we get to Mexico, our clothes will be out of style.
- You'd better take Mister Ed back to the stable, honey.
- Carol, Ed is going with us. And if you feel like crying, be my guest.
[...]