|Clipping from Jet, 2 April 1981.|
He also performed a gospel duet with Loretta Lynn. This is probably the performance that received "the standing ovation" mentioned here (sub Wish You Were Here Tonight).
Update 25 November 2013:
The website of the Country Music Hall Of Fame - surprisingly - offers a 30-second clip from the show. It indeed turns out to be a duet on a 'southern gospel' tune (written by Hank Williams): I'll Fly Away.
It was indeed a medley, with I'll Fly Away, Amazing Grace and an unidentified third gospel song:
[Video was deleted from YouTube]
Off topic: also read this.