It's the Great Pumpkin, Charlie Brown (1966)

In this timeless story, the spotlight is on Linus, the thumb-sucking, blanket-clutching character, and his heartfelt belief in the "Great Pumpkin." When Linus realizes that he stands alone in his conviction about the mythical creature, he embarks on a mission to demonstrate that the Pumpkin is real—by spending the night alone in a pumpkin patch.