Trikaya Sutra
The Three Kaya Sutra or Sūtra of the Three Bodies, (Skt. Trikāyasūtra, Tib. སྐུ་གསུམ་པའི་མདོ) contains an explanation of the three kayas: nirmanakaya, sambhogakaya and dharmakaya by the buddha, answering a question of the bodhisattva Kshitigarbha.