This conversation takes place at the very end of The Voyage of the Dawn Treader:
“Oh, Aslan,” said Lucy. “Will you tell us how to get into your country from our world?”
“I shall be telling you all the time,” said Aslan. “But I will not tell you how long or short the way will be; only that it lies across a river. But do not fear that, for I am the great Bridge Builder. And now come; I will open the door in the sky and send you to your own land.”
“Please, Aslan,” said Lucy. “Before we go, will you tell us when we can come back to Narnia again? Please. And oh, do, do, do make it soon.”
“Dearest,” said Aslan very gently,”you and your brother will never come back to Narnia.”
“Oh, Aslan!” said Edmund and Lucy both together in despairing voices.
“You are too old, children,” said Aslan, “and you must begin to come close to your own world now.”
“It isn’t Narnia, you know,” sobbed Lucy. “It’s you. We shan’t meet you there. And how can we live, never meeting you?”
“But you shall meet me, dear one,” said Aslan.
“Are–are you there too, Sir?” said Edmund.
“I am,” said Aslan. “But there I have another name. You must learn to know me by that name. This was the very reason why you were brought to Narnia, that by knowing me here for a little, you may know me better there.”
