During his visit to JRE Group of Institutions a few years ago, Dr. Philip Kotler spoke about the 5th P of marketing:

I’ve added to the 4ps a new p. you know the 4p’s is what marketers put together in a marketing plan; they have to describe the product, the price, the place, and the promotion. so the fifth I’ve added is purpose.

It’s around the five minute mark in this video: Dr.Philip Kotler’s visit to JRE Group of Institutions Campus on March 15,2013 – YouTube