SB 4.13.27
rajan havimsy adustani
sraddhayasaditani te
chandamsy ayata-yamani
yojitani dhrta-vrataih
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O King, we know that the paraphernalia to perform the sacrifice is well collected by you with great faith and care and is not polluted. Our chanting of the Vedic hymns is also not deficient in any way, for all the brahmanas and priests present here are expert and are executing the performances properly.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
It is the practice of the brahmanas conversant with the science to pronounce a Vedic mantra in the right accent. The combination of the mantra and Sanskrit words must be chanted with the right pronunciation; otherwise it will not be successful. In this age the brahmanas are neither well versed in the Sanskrit language nor very pure in practical life. But by chanting the Hare Krsna mantra one can attain the highest benefit of sacrificial performances. Even if the Hare Krsna mantra is not chanted properly, it still has so much potency that the chanter gains the effect.