This wall decal is almost right, but not quite. The actual quote from Chapter 8 of the original book, "Winnie-The-Pooh", is "Christopher Robin was sitting outside his door, putting on his Big Boots. As soon as he saw the Big Boots, Pooh knew that an Adventure was going to happen..."
This one seems to pop up a lot. Here's a version of it next to Milne smoking a pipe. Here's a version that someone made into a YouTube video. But it doesn't come from any of the Disney Pooh movies, and it's definitely not from an Milne book. It's like anything twee can count as a Pooh quote. Plus, 'ill' is a sickness without an apostrophe. Just saying.