Who wrote it?

Impromptu in Gb, Op. 90 No. 3 Franz Schubert (1797-1828)

"Fairest Lord Jesus"

Improvisation

One morning, Schubert brought singer Michael Vogl several songs for his perusal. Busy at the moment, Vogl set them aside and examined them later when he had opportunity. He liked one especially, but it was too high for him, so he transposed it and had a (hand) copy made. A couple weeks later he, Schubert and some friends were enjoying a musical evening together. Something new was asked for, and without comment Vogl placed Schubert’s song on the piano (in its new key, and someone else’s handwriting). When Schubert heard the piece, he exclaimed "H’m! Pretty good song! Who wrote it?"