4.
The Discourse on the Cloth
1104.
"Monks, when one's garment or head is on fire, what should be done?"
"Venerable sir, when one's garment or head is on fire, for the quenching of that very garment or head, exceeding desire and effort and endeavour and enthusiasm and unremitting and mindfulness and full awareness is to be done."
"Monks, having disregarded and not attended to the burning garment or head, for the full realisation as they really are of the four noble truths not yet fully realised, exceeding desire and effort and endeavour and enthusiasm and unremitting and mindfulness and full awareness is to be done. Which four? The noble truth of suffering, etc. the noble truth of the practice leading to the cessation of suffering.
"Therefore, monks, exertion is to be done regarding 'This is suffering', etc. exertion is to be done regarding 'This is the practice leading to the cessation of suffering.'" The fourth.