Here is a note I got from one of the artists on the above web page where I found the lyrics - it is in response to my query about from whence the song came and if there are more lyrics to it.
I first heard H-O Abha-Inn on a CD called Celtic Cradle by Jill Rogoff. It's available through Alcazar Records and I'd highly recommend it. Normally we (Jill and I) both loop it to draw it out a bit (first 4 lines, 2 lines, first 4 lines again, the 2 lines and the first 4 one last time) but as far as I know there aren't any additional lyrics. Noirin ni Riain also sings it as part of a lullaby set on her recording Celtic Soul. It sounds completely different. My version, recorded on Brigit's Well, is naturally my favorite! Hope this helps, Barbary