I believe you're referring to a line of Gandalf's from An Unexpected Journey, the first part of Peter Jackson's Hobbit film trilogy, which featured quite prominently in the announcement trailer:

Gandalf: You'll have a tale or two to tell of your own when you come back.

 

Bilbo: Can you promise that I will come back?

 

Gandalf: No. And if you do, you will not be the same.

 

^{The Hobbit: An Unexpected Journey (2012)}

As best I recall, this line does not appear in The Hobbit, nor in any of Tolkien's other works. There's a faintly similar line at the end of the book, where Gandalf reflects on Bilbo's development:

Gandalf looked at him. "My dear Bilbo!" he said. "Something is the matter with you! You are not the hobbit that you were."

 

^{The Hobbit Chapter 19: "The Last Stage"}

I believe you're referring to a line of Gandalf's from An Unexpected Journey, the first part of Peter Jackson's Hobbit film trilogy, which featured quite prominently in the announcement trailer:

Gandalf: You'll have a tale or two to tell of your own when you come back.

Bilbo: Can you promise that I will come back?

Gandalf: No. And if you do, you will not be the same.

^{The Hobbit: An Unexpected Journey (2012)}

As best I recall, this line does not appear in The Hobbit, nor in any of Tolkien's other works. There's a faintly similar line at the end of the book, where Gandalf reflects on Bilbo's development:

Gandalf looked at him. "My dear Bilbo!" he said. "Something is the matter with you! You are not the hobbit that you were."

^{The Hobbit Chapter 19: "The Last Stage"}

I believe you're referring to a line of Gandalf's from An Unexpected Journey, the first part of Peter Jackson's Hobbit film trilogy, which featured quite prominently in the trailer:

Gandalf: You'll have a tale or two to tell of your own when you come back.

Bilbo: Can you promise that I will come back?

Gandalf: No. And if you do, you will not be the same.

^{The Hobbit: An Unexpected Journey (2012)}

As best I recall, this line does not appear in The Hobbit, nor in any of Tolkien's other works. There's a faintly similar line at the end of the book, where Gandalf reflects on Bilbo's development:

Gandalf looked at him. "My dear Bilbo!" he said. "Something is the matter with you! You are not the hobbit that you were."

^{The Hobbit Chapter 19: "The Last Stage"}

I believe you're referring to a line of Gandalf's from An Unexpected Journey, the first part of Peter Jackson's Hobbit film trilogy, which featured quite prominently in the announcement trailer:

Gandalf: You'll have a tale or two to tell of your own when you come back.

Bilbo: Can you promise that I will come back?

Gandalf: No. And if you do, you will not be the same.

^{The Hobbit: An Unexpected Journey (2012)}

As best I recall, this line does not appear in The Hobbit, nor in any of Tolkien's other works. There's a faintly similar line at the end of the book, where Gandalf reflects on Bilbo's development:

Gandalf looked at him. "My dear Bilbo!" he said. "Something is the matter with you! You are not the hobbit that you were."

^{The Hobbit Chapter 19: "The Last Stage"}