Sabine Devieilhe, K.294
1778, Mannheim, Mozart to his father:
"...'Non so d’onde viene' which has been so charmingly composed by Bach. Just because I know that of Bach so well, and it pleases me and haunts my ear, I wished to try if, in spite of all this, I could succeed in writing an aria totally unlike the other..."
Mozart resolved to write it for his student, who is almost certainly his lover as well, Mademoiselle Weber.