Devibhagavatapurana 9.16.31

9.16.31

daivaṃ ca durnivāryaṃ ca na ca daivātparo balī |
jagatprasūṃ mayi nyasya chāyāṃ rakṣāntike'dhunā ||

The course of Destiny is irresistible; none else is more powerful than Time, Fate. So give over your Sîtâ, the World Mother to me and keep with you this Chhâyâ Sîtâ (the shadow Sîtâ; the false Sîtâ). When the time of Sîtâ’s ordeal by fire will take place I will give Her back to you. The Devas united have sent me to you. I am not really a Brâhmin; but I am Agni Deva (eater of oblations).” Râmachandra heard Fire and gave his assent. But his heart shattered. He did not speak of this to Laksmana. By the yogic power Agni (Fire) created a Mâyâ Sîtâ. This Mâyâ Sîtâ, O Nârada, was perfectly equal to the real Sîtâ. Fire, then, handed this Mâyâ Sîtâ to the hands of Râmachandra. Hûtâsana (fire) took the real Sîtâ and said, “Never divulge this to any other body” and went away. What to speak of divulging the secret to any other body, Laksmana even could not know it. By this time Râma saw one deer, made of all gold. To bring that deer carefully to her, Sîtâ sent Râmachandra with great eagerness. Putting Sîtâ under Laksmana’s care, in that forest, Râma went himself immediately and pierced the deer by one arrow. That Mâyâ mrîga (the deer created by magic powers) on being pierced, cried out “Ha Laksmana!” and seeing Hari before him and remembering the name of Hari, quitted his life. The deer body then vanished; and a divine body made its appearance in its stead. This new body mounting on an aerial car made of jewels, ascended to Vaikuntha. That Mâyik (magic) deer was in its previous birth, a servant, of the two gate-keepers of Vaikuntha; but, for the sake of some emergency, he had to take up this Râkhsasa birth. He again became the servant of two door-keepers of Vaikuntha. On the other hand Sîtâ Devî, hearing the cry “Ha Laksmana!” became very distressed and sent Laksmana in search of Râma. No sooner did Laksmana get out of the hermitage, the irresistible Râvana took away Sîtâ gladly to the city of Lanka (Ceylon). Now Râmachandra, seeing Laksmana on the way in the forest, became merged in the ocean of sorrows and without losing any time came hurriedly to the hermitage where he could not find Sîtâ. Instantly he fell unconscious, on the ground; and, after a long time, when he regained his consciousness, he lamented and wandered here and there in search of Her. After some days on the banks of the river Godâvarî, getting the information of Sîtâ, he built a bridge across the ocean with the help of His monkey armies. Then he entered with his army into Lanka and slew Râvana with arrows with all his friends. When Sîtâ’s ordeal by fire came, Agni (Fire) handed over the real Sîtâ to Râmachandra. The Shadow Sîtâ then humbly addressed Agni and Râma Chandra, “O Lord! What am I to do now? Settle my case.”