It's Zero Mostel as a guest on The Dean Martin Show when he performs the song "Do You Love Me?" from Fiddler on the Roof, singing it with Kay Medford, who was a semi-regular on the TV series..
Medford was in the original Broadway cast of Bye Bye Birdie, playing the role of Dick Van Dyke's Mama. She was a wonderful comic actress, though not much of a singer. (In fact, that's why they cut the wonderful song, "A Mother Doesn't Matter Anymore," which finally got added back into the show for the TV movie with Jason Alexander, and Tyne Daly as Mama.) But "Do You Love Me?" doesn't require much singing on the part of the wife.
I was going to say, "on the part of Tevye's wife Golde," but they don't really perform this as Tevye and Golde. Rather they play it as a modern-day couple, and it's a bit odd for that -- especially because Medford in particular plays it very laconic and almost realistic, rather than incredulous and bewildered as the comic number it is. I can't say that I think the interpretation and context helps the song much, but she's a fine actress and most-happily of all, Mostel gives us as close to Tevye has you can expect, and it still has a sweet charm. And ultimately, just having footage of Zero Mostel on camera singing the song is treat enough.