Digha Nikaya 2:51
SUJATOPuna caparaṁ, bhikkhave, bhikkhu seyyathāpi passeyya sarīraṁ sivathikāya chaḍḍitaṁ ekāhamataṁ vā dvīhamataṁ vā tīhamataṁ vā uddhumātakaṁ vinīlakaṁ vipubbakajātaṁ.
Furthermore, suppose a mendicant were to see a corpse discarded in a charnel ground. And it had been dead for one, two, or three days, bloated, livid, and festering.