J.S. Bach: Prelude in C minor, BWV 999

Based on Thomas Kohlhase [de], the 1998 edition of the Bach-Werke-Verzeichnis indicates that the piece likely originated in Bach's Köthen period, that is, between 1717 and 1723. Christoph Wolff and Walter Emery estimated that the composition may have originated from Bach's Köthen period to the early years of his Leipzig period, which began in 1723, based on similarities with the Preludes and Fugues in The Well-Tempered Clavier. (From Wikipedia)