Further discussion of variants, and links to earlier discussions and examples here and elsewhere are in this thread:  Lyr/Chords Req: The Nightengale Sings.

I somehow missed the DT file that GUEST points to last time around; it was transcribed from an American recording and no tune or traditional source is indicated.  It is very close, aside from some minor alterations in wording and the order of verses (and the inclusion of two additional verses) to the set published by Baring Gould in Songs of the West (revised edition, 1905).  Baring Gould had -to begin with- only the tune, and printed the text published by Robert Bell in his revision of Dixon's Ancient Poems, Ballads and Songs of the Peasantry of England (1857):  The Sweet Nightingale; or, Down in Those Valleys Below  (the link is to an e-text at  Poets' Corner).

He later got a number of texts from tradition, but perhaps they were a little too suggestive for publication at that time!  He notes that the song in that form derives from a piece written by Bickerstaff for Arne's opera Thomas and Sally (1760), a dialogue between the Squire and Sally, which begins:

Well met, pretty maid;
Pray don't be afraid,
I mean you no mischief, I vow.
Pshaw! what is't you all?
Come, give me your pail,
I'll carry it up to your cow.

If Bickerstaff followed the story we are familiar with, he presumably based it on earlier examples, which as Bruce Olson pointed out in an earlier discussion, go back to the early 17th century.  Arne's tune seems not to have made it into tradition.