One of the most famous images of Winnie the Pooh - as the bear plays "Poohsticks" with Piglet and Christopher Robin - is expected to fetch more than £100,000 at auction.
The illustration by EH Shepard - first published in 1928 - has been in a private collection for more than 40 years but will now be sold by Sotheby's next month.
Shephard's ink drawing featured in the AA Milne book The House At Pooh Corner, for Chapter 6 "in which Pooh invents a new game and Eeyore joins in".
It accompanies the closing scene of the chapter where the three characters stand on the "Poohsticks" bridge as the mood changes from the high excitement of their new game to a more wistful atmosphere.
"For a long time they looked at the river beneath them, saying nothing, and the river said nothing too, for it felt very quiet and peaceful on this summer afternoon," Milne wrote.
The drawing will feature in Sotheby's sales of English literature, history, children's books and illustrations on December 9 and is estimated to sell for between £100,00 and £150,000.
The auction firm said: "The illustration can be counted among the most familiar, and most loved, cultural references in English literature."
The original wooden crossing on which the illustration is based - known as Posingford Bridge, at Hartfield Farm, Sussex - had fallen into disrepair by the 1970s.
It was carefully restored and reopened by Christopher Milne - the author's son who inspired the character of Christopher Robin - in May 1979 at a ceremony where it was called "as important a bridge as any in the world". It was completely rebuilt in 1999.