Perhaps it was in a songbook by Nóirín Ní Riain, one of a number of people who have recorded Seoladh na nGamhna. I don't recall what version she has.

A listing for a recording by Nóirín Ní Riain describes the song thus: "A song with mystical love, about a man that sees his lover as he drives cattle through the pasture. They spend a night together and he leaves her with this final blessing; 'Here's a little kiss for you on the tip of my fingers, and O my Love, My five hundred blessings be with you!'"

Susan McKeown's lyrics of Seoladh na nGamhna and real-audio are on the web. McKeown writes, "I recently rediscovered Mary O'Hara on a Rykodisc re-release of a 1960 recording [Down by the Glenside: Songs of Ireland], and through her this haunting song. Mary got the song from Liam Clancy, whose translation this is*. The song comes from Mahonbridge in County Waterford."

*trans. by Liam Clancy:
Late one evening by the glenside and I driving the cattle to pasture
I saw beside me a beautiful woman, chalk-white, gentle and modest
I gently asked the beautiful maiden "What brought you here?"
"Looking for the calves I left home, and not a one have I found"

"There's a fragrant tree in the angle of the wood, and let us go there
Where the music of the birds will put us to sleep
And we'll get the calves tomorrow
I'll get permission from the keeper of the wood
To give them a day's portion of grass."

Seoladh na nGamhna lyrics, not all identical, are also to be found at http://www.angelfire.com/ri/domhan/clars09.html
as recorded by Birkin Tree
http://www.acronet.net/~robokopp/eire/seoladh.htm
Liam Harte's Gaelic song pages