Question: Which epic poem was "Ave Maria" loosely based on, which is used by Wilfred Jackson in Walt Disney's "Fantasia"?

Context paragraphs:
The Pied Piper (1933 film): The Pied Piper is a 1933 American Pre-Code animated short film based on the story of the "Pied Piper of Hamelin".  The short was produced by Walt Disney Productions, directed by Wilfred Jackson, and released on September 16, 1933, as a part of the Silly Symphonies series.

Cinderella (1950 film): Cinderella is a 1950 American animated musical fantasy film produced by Walt Disney and originally released by RKO Radio Pictures.  Based on the fairy tale "Cinderella" by Charles Perrault, it is the twelfth Disney animated feature film.  Directing credits go to Clyde Geronimi, Hamilton Luske, and Wilfred Jackson.  Songs were written by Mack David, Jerry Livingston, and Al Hoffman.  Songs in the film include "Cinderella", "A Dream is a Wish Your Heart Makes", "Sing Sweet Nightingale", "The Work Song", "Bibbidi-Bobbidi-Boo", and "So This is Love".  It features the voices of Ilene Woods, Eleanor Audley, Verna Felton, Rhoda Williams, James MacDonald, Luis van Rooten, Don Barclay, Mike Douglas, and Lucille Bliss.

The Country Cousin: The Country Cousin is a Walt Disney animated short film released on October 31, 1936 by United Artists.  The winner of the 1936 Academy Award for Best Animated Short Film, the film was produced by Walt Disney, directed by Wilfred Jackson, and animated by Art Babbitt and Les Clark.  As is true for most cartoons in the "Silly Symphonies" series, "The Country Cousin" was built around a musical score, which was written by Leigh Harline.  The film's story was based on one of Aesop's Fables, The Town Mouse and the Country Mouse.  It was accompanied by a storybook for young children, which was usual for the most popular "Silly Symphonies".

The Wise Little Hen: The Wise Little Hen is a Walt Disney's Silly Symphonies cartoon, based on the fairy tale "The Little Red Hen".  This cartoon marked the debut of Donald Duck, dancing to the Sailor's Hornpipe.  Donald and his friend Peter Pig try to avoid work by faking stomach aches until Mrs. Hen teaches them the value of labor.  This cartoon was released on June 9, 1934.  It was animated by Art Babbitt, Dick Huemer, Clyde Geronimi, Louie Schmitt, and Frenchy de Tremaudan (with assistance from a group of junior animators headed by Ben Sharpsteen) and directed by Wilfred Jackson.  It was also adapted as a Sunday comic strip by Ted Osborne and Al Taliaferro.

The New Spirit: The New Spirit is a 1942 American animated short film produced by Walt Disney Productions and the U.S. Department of the Treasury, and released by the War Activities Committee of the Motion Pictures Industry.  The cartoon, which stars Donald Duck, was the first film created as part of Walt Disney's World War II propaganda production.  It was commissioned by Henry Morgenthau, Jr., then Secretary of the Treasury, to encourage American citizens to pay their income tax in support of the war effort.  The film was directed by Wilfred Jackson and Ben Sharpsteen, and features Clarence Nash as the voice of Donald, Fred Shields as the radio announcer, and Cliff Edwards singing the theme song.

Ave Maria (Schubert): "Ellens dritter Gesang " ("Ellens Gesang III ", D. 839, Op.  52, No. 6, 1825), in English: "Ellen's Third Song", was composed by Franz Schubert in 1825 as part of his Opus 52, a setting of seven songs from Walter Scott's popular epic poem "The Lady of the Lake", loosely translated into German.

The Night Before Christmas (1933 film): The Night Before Christmas is a 1933 American Pre-Code animated short film produced by Walt Disney Productions and released by United Artists.  Part of the "Silly Symphony" series, the film is an adaptation of Clement Clarke Moore's poem "A Visit from St. Nicholas", popularly called "The Night Before Christmas".  The film was directed by Disney animator Wilfred Jackson.

Garshaspname: Garshāspnāme (Persian: گرشاسپ‌نامه‎ ‎ ) is an epic poem by Asadi Tusi.  It has been described as one of the best epic poems in Persian literature, comparable to Shahname, by Jalal Khaleqi-e Motlaq, and the most important work of Asadi Tusi.  Asadi Tusi completed the poem in 1066 AD and dedicated it to a certain "Abū Dolaf", the ruler of "Nakjavān" (nothing is known about him).  The poem is also translated to other languages such as French and German.  It seems that Asadi Tusi wrote this poem based on a written source.  Like Shahname, it contains few Arabic loan-words and consists of some 9,000 verses.  The main hero of this epic poem is Garshasp, the son of Etret, and grandson of Šam.  The poem begins with the story of Jamshid and Zahhak.  Jamshid is overthrown by Zahhak and flees to Zabolistan.  In Zabolistan, Jamshid falls in love with an unnamed daughter of Kurang, the king of Zabolistan, and she bore a child for Jamshid, named Tur (not to be confused with Tur, the son of Freydun).  Jamshid flees again to China.  Garshasp is actually the grandson of Tur's grandson.

Snow White and the Seven Dwarfs (1937 film): Snow White and the Seven Dwarfs is a 1937 American animated musical fantasy film produced by Walt Disney Productions and originally released by RKO Radio Pictures.  Based on the German fairy tale by the Brothers Grimm, it is the first full-length cel animated feature film and the earliest Disney animated feature film.  The story was adapted by storyboard artists Dorothy Ann Blank, Richard Creedon, Merrill De Maris, Otto Englander, Earl Hurd, Dick Rickard, Ted Sears and Webb Smith.  David Hand was the supervising director, while William Cottrell, Wilfred Jackson, Larry Morey, Perce Pearce, and Ben Sharpsteen directed the film's individual sequences.

Wilfred Jackson: Wilfred Jackson (Chicago, Illinois, January 24, 1906 – Newport Beach, California, August 7, 1988) was an American animator, arranger, composer and director best known for his work on the "Mickey Mouse" and "Silly Symphonies" series of cartoons and the two segments "Night on Bald Mountain" and "Ave Maria" of "Fantasia" from Walt Disney Productions.  He was also instrumental in developing the system with which Disney added music and sound to Steamboat Willie, the first Mickey Mouse cartoon.  Several of the Silly Symphony shorts he directed, including "The Old Mill" (1937), won Academy Awards during the 1930s.  Starting with "Snow White and the Seven Dwarfs" in 1937 he directed sequences in many of the major Disney animated features up to "Lady and the Tramp" in 1955, including all of the animated sequences in "Song of the South" (1946).  He later moved into television, producing and directing for Disney's Disneyland series.  After continuing health issues he retired in 1961.  Wilfred Jackson died at age 82 in 1988.

Supporting paragraphs: Wilfred Jackson Ave Maria (Schubert)
Answer: The Lady of the Lake