"I Can't Carry It for You... but I Can Carry You."
From Tolkien Gateway
"I Can't Carry It for You... but I Can Carry You." is the fifty-first scene of The Lord of the Rings: The Return of the King and the sixty-sixth scene of The Lord of the Rings: The Return of the King (extended edition).
In the books, it is in part 2 of ROTK.
It is said by Samwise Gamgee, in Mordor, as he and Frodo Baggins approach Mount Doom, referencing to the fact that Sam can not carry the One Ring, but he can carry Frodo himself, and he does.