I'm not if this has been asked about before, but anyway it's the song 'Tá mé/Táim Sínte ar do Thuama' as sung by the late lamented Diarmuid Ó Súilleabháin. There seem to be a couple of versions of it, but they don't seem to tally with what he is singing here. Could someone help please ?

https://www.youtube.com/watch?v=4Y2O42Bg6q4

There are often slightly different versions of old songs.
I'm not familiar with the song so I have nothing to compare it to.
Wikipedia gives a list of musicians who have recorded it.