When Lord Ramacandra tested the body of Sita, it was the false, illusory Sita that entered the fire. At that time the fire-god brought the original Sita from his abode and delivered her to Lord Ramacandra

Expressions researched:
"When Lord Rāmacandra tested the body of Sītā, it was the false, illusory Sītā that entered the fire. At that time the fire-god brought the original Sītā from his abode and delivered her to Lord Rāmacandra"

Sri Caitanya-caritamrta

CC Madhya-lila

“When he was petitioned by mother Sītā, the fire-god, Agni, brought forth an illusory form of Sītā, and Rāvaṇa, who had ten heads, kidnapped the false Sītā. The original Sītā then went to the abode of the fire-god. When Lord Rāmacandra tested the body of Sītā, it was the false, illusory Sītā that entered the fire. At that time the fire-god brought the original Sītā from his abode and delivered her to Lord Rāmacandra.”.

CC Madhya 9.211-212, Translation and Purport

“When he was petitioned by mother Sītā, the fire-god, Agni, brought forth an illusory form of Sītā, and Rāvaṇa, who had ten heads, kidnapped the false Sītā. The original Sītā then went to the abode of the fire-god. When Lord Rāmacandra tested the body of Sītā, it was the false, illusory Sītā that entered the fire. At that time the fire-god brought the original Sītā from his abode and delivered her to Lord Rāmacandra.”

These two verses are taken from the Kūrma Purāṇa.