What is the origin of the Buddhist expression "Practice as if your hair is on fire"?

I remember this phrase but I have not been able to locate it in the texts. I do not recall the correct words but it's something like this: *"Meditate/practice as if your hair is/were on fire"*. I have searched on Buddhism SE and on Google and found the phrase mentioned a couple of times but no solution to the origin of it. This article mentioned by Matthew says; > "Practice like your hair is on fire! > >A traditional aphorism, which probably goes back to Buddhism in India. Gelek Rinpoche makes it the theme of his recent article in Buddhadharma. And it shows up in the Zen tradition and elsewhere." And this article says: >Zazen makes waiting into a science. I'm intrigued by the Zen injunction "Sit as if your hair were on fire." Still no solution to the origin of the phrase. I'm looking for valid sources such as the *Theravadan, East Asian and Tibetan texts*. Thank you for your time.