The earliest sample I could find is from Biz Markie's "Romeo and Juliet" (1991):
Joe Budden uses the Wither's song on "The Future" (2006) from his Mood Muzik 2: Can It Get Any Worse?:
Tech N9ne mostly used the least interesting part of the riff in "Last Words" from his 2008 album Killer:
Hilarious album cover, though.
Outerspace sample the song on their "What the Future Holds" from their 2008 album God's Fury, actually including some of Bill's lyrics:
Bitches say I'm the cool ass.
* Don't judge that reference.