Two sources of Fantasia 3 are known but only the transcribed one here is ascribed and differs significantly from the other one. The first 30 and last 40 bars are nearly identical, but the  material in between is different and much more extended in the transcribed one.

The source of this Fantsia is: Musik Bibliothek des Stadt Leipzig, Germany; MS II.6.15.  pp 56-58, c. 1619