This talk by President Kimball is probably the one I remember when I was a child. I remember a lot of "Do It" in the talk so it probably is this talk. It has stuck in my mind for a very long time. I just always remember, "Do It".
"No matter what the cost in toil or sacrifice, we must 'do it.' That is one of my favorite phrases: 'Do It.'"
(Spencer W. Kimball, "Becoming the Pure in Heart", April 1978)
