There are actually three prophesies that Mr. and Mrs. Beaver relate to the children; all of them can be found in Chapter 8, and address the end of evil as represented by the White Witch's reign. The first tells about the coming of Aslan, and how he will set all things right. The prophesy is told in rhyme, which Mr. Beaver recites, saying,
"Wrong will be right, when Aslan comes in sight.
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."
The second prophesy continues along the same theme, and is also told in rhyme. Mr. Beaver again recites,
"When Adam's flesh and Adam's bone
Sits at Cair Paravel in throne,
The evil time will be over and done."
The final prophesy offers further detail of the demise of evil as represented by the White Witch. Unlike the others, it is not told in rhyme. Mr. Beaver relates this prophesy, saying,
"...when two Sons of Adam and two Daughters of Eve sit in those four thrones, then it will be the end not only of the White Witch's reign but of her life."
As each edition of the work may vary in its pagination, I have not given you page numbers. As I mentioned, all the quotes are in Chapter 8; the first two are in rhyme and are in italics, so they should be easy to find. The third is just a little past the midpoint of the chapter, in the paragraph which begins, "Because of another prophecy..."