This is on the same theme as All good things come to an end. The words can be
found in the chorus of _There is a Tavern in the Town_ :

> Fare thee well, for I mast leave tee,
> Do not let this parting grieve thee,
> And remember that the best of friends must part.
> Adieu, kind friends, adieu, adieu, adieu, adieu,
> I can no longer stay with you;
> I’ll hang my harp on the weeping willow tree,
> and may the world go well with thee.

In passing, the hang one’s harp on a willow tree is a to put an end to song
and mirth. The source is Psalms, cxxxvii, 2.