Source: Hitching a ride. - Funny Pictures
Stashed in: Lolcats!, gifs, Goats!
YouTube videos of cats riding things.
A Tumblr search of "cats riding things" reveals... only a video version of your gif.
Luckily, Memetastic has Paula Deen riding a cat:
Clint Dempsey goal vs Portgual USA World Cup 2014 gif / gfycat
We need engineers that can build stuff and solve problems. ~Bill Nye the Science Guy
WAT meme gun gif
I'm no lady. ~Brienne of Tarth gif