This is supposedly ODB's audition tape for the character of Mr. Ed (for the coming remake). It's all of his lines sort-of pasted together, which doesn't make much sense linearly, but because it's ODB comes off farrrrr more hilariously than it would otherwise. Of course, it's quite possible it isn't ODB:
From: WFMU'S BEWARE OF THE BLOG:
May 26, 2005
Last year, when Ol' Dirty Bastard died, there had been rumors about him possibly doing the the voice of Mister Ed in the Fox TV remake of the series. Then today in my inbox arrived this mp3 (right-click to download) of the alleged audition. Is it true? Did Dirty really try out for the role of talking horse?
Either way, it's incredible.