CC Madhya 1.117
māyā-sītā nileka rāvaṇa, tāhāte likhana
At Rāmeśvara, Śrī Caitanya Mahāprabhu had a chance to read the Kūrma Purāṇa, in which He discovered that the form of Sītā kidnapped by Rāvaṇa was not that of the real Sītā but a mere shadow representation.
The Kūrma Purāṇa states that this shadowy Sītā was placed into a fire as a test of chastity. It was Māyā-sītā who entered the fire and the real Sītā who came out of the fire.