That's a prayer for those who are already dead.
I haven't found a suitable line out of Irish mythology yet, but here's the one I got from Finnish epic poetry, modified by omission of some lines and changing others where noted in brackets:
From "The Healing of Wainamoinen"
Kalevala, Runo IX
Crimson streamlet, cease thy flowing
Blood of ages, stop thy coursing
From the veins of [fallen warriors];
Stand like heaven's crystal pillars,
Stand like columns in the ocean,
Stand like birch-trees in the forest,
Like the tall reeds in the marshes,
Like the high-rocks on the sea-coast,
Stand by power of mighty magic!
Should perforce thy will impel thee,
Flow thou on thine endless circuit,
Through the veins of [fallen wariors],
Through the bones, and through the muscles,
Through the lungs, and heart, and liver,
Of the mighty [swordsman hero];
Better be the food of heroes,
Than to waste thy strength and virtue
On the meadows and the woodlands,
And be lost in dust and ashes.
Flow forever in thy circle;
Thou must cease this crimson out-flow;
Cease thy flow, by word of magic
Thus to save the wounded hero.
I think Alric uses the Lord's Prayer in Old English, and I know there was someone else who uses an actual Christian prayer of healing from (I believe) the traditional Catholic healing service. Make something like that up themed towards, well, whatever or whoever your character would pray to or invoke.