Ná h-abair-se bréithir móir...

Ná h-abair-se bréithir móir
ná h-abair nach tibre chóir,
ór is nár a rádh co tenn
muna fedtar a comall.

(not * say [emphatic] * words * great
not * say * which-not * you might give * rightly
for * is * shame * its * saying * with * force
if not * is possible* its * fulfillment)

Don't make grand statements
and don't promise what you can't rightly give,
for it is shameful to boast of things
that you cannot deliver.

This is the sixth stanza in the poem "Fionn's Advice to Mac Lugach" at the beginning of "Acallam na Senórach". See also "Dá trian do mhíne re mnáibh" and "Bid co h-eistechtach cailli" in this collection.