Although written for Clavier or Piano, Johann Sebastian Bach's fugues can readily be arranged for different instrumental groups. Fugue No. 24 from Book 1 (of "the 48") is in four parts, and easily converted into an arrangement for String Quartet. See the "Downloads & Links" section, or see the sheet music score below. Here is the original piano/keyboard version of the fugue no.24 from book 1 of the fugue for reference, and here is its corresponding Prelude no.24 from book 1 in the same key of B minor.
The audio controls below allow you to play the mp3 version of Bach's Fugue No.24 in Bm from book 1 (for String Quartet) or you can download the MP3 file. You can also download the midi version of Bach's Fugue No.24 in Bm from book 1 (for String Quartet).
The image below is the first page of the sheet music score, and here you can download the full sheet music score for Bach's Fugue No.24 from book 1 for string quartet in PDF format. The four instrumental parts are as follows: Violin 1, Violin 2, Viola and Cello.