This comes from a show by a Canadian Klezmer group, Beyond the Pale. They were doing a show at a coffeehouse in Berkeley, California. The Freight and Salvage. It turned out that legendary performer Theodore Bikel was in the audience, so they invited him up on stage and asked him to play a number.
It should be noted that this is from just five years ago, when Mr. Bikel was 86 at the time. And had no vocal warm-up or rehearsal. It's just a little, Russian folk song, and he sits down, plays and sings the bejeepers out of it, the mark of someone who has been doing this for probably close to 70 years and has a pretty good idea how it's done. The band joins in and does a nice job filling in an impromptu backup, but they know they're with someone in another league.
Before they help him head back to his seat in the audience...