Is there an authentic source for the below story?
The story is told of a man who asked Rabbi Yisroel Salanter a question. "Rebbi, I have only 15 minutes a day to learn Torah. What should I study?" Replies Rabbi Salanter, "Learn Mussar !" "Why, mussar?" asked the man. "Because," responded Rabbi Salanter, "if you start learning mussar, you'll realize that you have more than 15 minutes a day to learn!"