Bachman–Turner Overdrive - "Takin' Care of Business". [1973]. It reached #12 on the Billboard Hot 100, #6 on the Cash Box Top 100, and #3 on the Canadian RPM charts.

From Snopes:

The thing is, Bachman-Turner Overdrive, when I met them, they were across the hall, and they don't get high; they just eat a lot of pizza. And they wanted piano on this song, and I was across the hall doing commercials, which is what I did a lot for money back at that time; and they come in, and one of the engineers says, "Can you play on this tune?" And I said, "No," because no one knew that "Takin' Care of Business" was a big deal when [they were] making it, and I had hired like eight or ten people [to record commercials] and I [was] paying them by the nanosecond.

So to me, the most amazing part of this story is I go over to this studio — and the engineer's name is Buzz Richmond and he's a good guy — he says, "Can you please do this for 'em?" I says, "Okay, one time, and then I'm f***ing out of here." So Randy says — this is the part that kills him — "Do you want to hear this song?" and I said, "No, I don't have time to hear it."

So we both put on headphones, and then when he wanted me to play, he would point, and when he wanted me to stop, he put his hand across his throat. And so, the thing starts [imitates intro to "Takin' Care of Business"] and they point, and I go [imitates piano playing], and anyway, we get through the whole song, and I get up and leave. And he says, "How do you do that?" And I says, "I don't know; I've got this magic, man, you know. Gimme some money or something."

So I get ninety dollars, which is the legal fee for a union musician playing one session. Then later, one of the Allman Brothers says, "You know, man, you really got f***ed," and so he gave me a couple of grand.

That's B.T.O. They were Canada's answer to E.L.P. Their biggest hit was T.C.B. That was how we talked in the seventies. We didn't have a moment to spare.