Dolly Parton's sister is asking for prayers for the country icon a week after she postponed her Las Vegas residency due to unspecified "health challenges." "Last night, I was up all night praying for my sister,

"I ain't dead yet," Parton, 79, said in the caption to an Instagram video.

Worries for Parton intensified Tuesday after her sister made a post pleading for prayers, leading to an outpouring of concern.