Here are the lyrics as sung by Fred Cantwell on the album "Folk Songs of England, Ireland, Scotland and Wales: Songs of Seduction", collected by Alan Lomax:

As I was a walking one morning in May,
I saw a sweet couple together at play,
And the first was a fair lady, so beautiful and so fair,
The other was a soldier, a brave Grenadier.

CHORUS
But they kissed so sweet and comforting as they pressed to each other,
They went arming along the road like sister and brother,
They went arming along the road till they came to a spring,
Then they both sat down together, love, to hear the nightingales sing.

Then out of his knapsack he drew a long fiddle,
And he played to her such a merry tune that ever she did hear,
Oh he played to her such a merry tune, it caused the valley to ring,
"Oh, hark," replied the pretty maid, "Hear the nightingales sing!"

Now I'm off to India for seven long years
Drinking fine wine and whisky instead of strong beer
But if ever I should return again 'twill be in the Spring
And we'll both sit down together love to hear the nightingales sing.

Then up spake the fair lady, oh, soldier, tarry with me,
No, no, replied the soldier, how ever can that can be,
For I've got a little wife at home in my home country,
And she is the fairest little woman that your eyes ever see.