CC Madhya 9.206

tabe māyā-sītā agni kari antardhāna
satya-sītā āni’ dila rāma-vidyamāna
Word for word: 
tabe — at that time; māyā-sītā — the illusory form of Sītā; agni — the fire-god; kari — doing; antardhāna — disappearing; satya-sītā — real Sītā; āni’ — bringing; dila — delivered; rāma — of Rāmacandra; vidyamāna — in the presence.
Translation: 
When the illusory Sītā was brought before the fire by Lord Rāmacandra, the fire-god made the illusory form disappear and delivered the real Sītā to Lord Rāmacandra.