The eight-voice motet Ich lasse dich nicht (BWV Anh. 159) has been attributed both to J. S. Bach and to his father's cousin Johann Christoph Bach (1642-1703). A new look at the sources and transmission of the motet makes clear that the attribution to the older Bach was a nineteenth-century speculation that must be rejected. With the question of the motet's authorship reopened, the evidence shows that Ich lasse dich nicht is indeed by J. S. Bach. The oldest source, partly in Bach's hand, may be securely dated to the Weimar period, making the motet one of Bach's earliest extant vocal works. This dating challenges the widely-held assumption that Bach wrote all his motets in Leipzig, and forces a reevaluation of the dating of his other motets.