MEMPHIS, Tenn. — Isaac Hayes was being treated at a Memphis hospital Tuesday for exhaustion, his longtime songwriting partner said.

"He's just overworked and had been in Atlantic City performing, the D.C. area performing, and in Tunica (Miss.) a couple of nights ago. He was just overworked," David Porter told The Commercial Appeal newspaper.

"He's doing much better," Porter added.

It was not immediately known which hospital the soul singer had checked into. Calls to his agents were not returned.

Hayes, 63, is best known for his 1971 No. 1 hit "Theme From Shaft," from the Richard Roundtree film. The soundtrack won the Oscar for best musical score.

More recently, he was the voice of the character Chef on the TV show "South Park."

During his time as a backup artist at Stax Records in Memphis, he established a songwriting partnership with Porter, and in the 1960s they wrote such hits for Sam and Dave as "Hold On, I'm Coming" and "Soul Man."