This quote comes from Chapter 8 of The Lion, the Witch, and Wardrobe.
"Who is Aslan?" asked Susan.
"Aslan?" said Mr. Beaver. "Why, don't you know? He's the King. He's the Lord of the whole wood, but not often here, you understand. Never in my time or my father's time. But the word has reached us that He has come back. He is in Narnia at this moment. He'll settle the White Queen all right. It is He, not you, that will save Mr. Tumnus."
"She won't turn Him to stone too?" said Edmund.
"Lord love you, Son of Adam, what a simple thing to say!" answered Mr. Beaver with a great laugh. "Turn Him into stone? If she can stand on her two feet and look Him in the face it'll be the most she can do and more than I expect of her. No, no. He'll put all to rights as it says an old rhyme in these parts:
Wrong will be right, when Alsan comes in sight,"You'll understand when you see Him."
At the sound of His roar, sorrows will be no more,
When He bares his teeth, winter meets its death,
And when He shakes His mane, we shall have spring again.
"But shall we see Him?" asked Susan.
"Why, Daughter of Eve, that's what I brought you here for. I'm to lead you to where you shall meet Him, said Mr. Beaver.
"Is - is He a man?" asked Lucy.
"Aslan a man!" said Mr. Beaver sternly. "Certainly not. I tell you He is the King of the wood and the son of the great Emperor-beyond-the-sea. Don't you know who is the King of Beasts? Aslan is a lion - the Lion, the great Lion."
"Ooh!" said Susan, "I'd thought He was a man. Is He - quite safe? I shall feel rather nervous about meeting a lion."
"That you will, dearie, and no mistake," said Mrs. Beaver; "if there's anyone who can appear before Aslan without their knees knocking, they're wither braver than most or else just silly."
"Then He isn't safe?" said Lucy.
"Safe?" said Mr. Beaver; "don't you hear what Mrs. Beaver tells you? Who said anything about safe? 'Course He isn't safe. But He is good. He is the King, I tell you."