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.