From Muppet Wiki

Written by	Michael Silversher and Patty Silversher
Music by
Lyrics by
Date
Source
Publisher

Together Forever is sung by Elmo about his blanket in The Adventures of Elmo in Grouchland. Initially just sung in Elmo's bedroom, Elmo eventually gets his blanket wet and has to take it to the laundromat, where Big Bird, Telly Monster, Baby Bear, Bob, Luis, Gordon, Gina, Count von Count, and others join Elmo.