What is the origin of the Buddhist expression "Practice as if your hair is on fire"?
Tissa (Thag 1.39)   {Thag 39}
  
  As if struck by a sword,
  as if his head were on fire,
  a monk should live the wandering life
      — mindful —
  for the abandoning of sensual passion.


Source: http://www.accesstoinsight.org/tipitaka/kn/thag/thag.01.00x.than.html#passage-39