Sabrina: The Animated Series - Season 1 - Eps 54: Hexcalibur
Sabrina and Salem destroy Zelda's old magic book that was written and signed by Merlin himself. They travel back in time to the middle ages to when Merlin first wrote the book but a problem occurs and they go to far up to when Merlin was 12 yrs old. Back then he was an amatuer at magic and his friend (King) Dude Arthur was terrible at magic so Sabrina and Salem teach them and soon they find the mighty sword of Excalibur which they need to use to defeat the evil forces that threaten Arthur from becoming King. In the end they win and Merlin gives Sabrina a new replaceable magic book for Zelda. She and Salem go back and put it back on the shelf but when they accidently destroy all of Zelda's other books too the adventure starts all over again.
About Sabrina: The Animated Series

Title: Sabrina: The Animated Series
First Air Date: 1999-09-06
Last Air Date: 2000-02-27
Status: Ended
Rating: 6.7/10 (from 78 votes)
Language: ZH
Seasons: 2
Total Episodes: 65
Network: ABC UPN
Genres: Animation, Sci-Fi & Fantasy, Comedy, Family
Production Companies: Riverdale Productions, DiC Entertainment, Hartbreak Films, Cookie Jar Entertainment, Savage Studios
Synopsis
An animated prequel to the live-action show "Sabrina, the Teenage Witch," the series features 12-year-old Sabrina Spellman, who's half mortal and half witch. Though few people know of her powers, and her mortal uncle frequently warns her not to use her magic to solve problems, Sabrina still borrows spells from the Spookie Jar and gets into trouble with her friend Harvey.
Cast

Melissa Joan Hart
Hilda Spellman / Zelda Spellman (voice)

Nick Bakay
Salem Saberhagen (voice)

Emily Hart
Sabrina Spellman (voice)

Jay Brazeau
Uncle Quigley (voice)

Jason Michas
Slugloafe (voice)

David Sobolov
Spookie Jar (voice)

Chantal Strand
Gem Stone (voice)

Cree Summer
Chloe Flan (voice)

Bill Switzer
Harvey Kinkle (voice)

Bob Bergen
Tim (voice)