I never sing a song without finding out all I can about it -- back to the oldest written source if possible. I feel strongly about giving credit where it's due as well. I don't copy other singers intentionally.
Having said that I try to keep my introductions about a song brief -- so that people don't go home before they get what they came for. I credit the author if possible. If it's a traditional song I say where it comes from. Sometimes I add comments about where I first heard it and from whom -- but I consider this less important.

Sorry -- I realise that I don't actually say, "I got this from the singing of..." so maybe I'm raving again.
Cheers, Joy