Srimad Bhagavatam Canto 10, Chapter 07, Text 17

SB 10.7.17

vipra mantra-vido yuktas
tair yah proktas tathasisah
ta nisphala bhavisyanti
na kadacid api sphutam
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The brahmanas, who were completely expert in chanting the Vedic hymns, were all yogis fully equipped with mystic powers. Whatever blessings they spoke were certainly never fruitless.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Brahmanas fully equipped with the brahminical qualifications are always yogis fully powerful in mystic yoga. Their words never fail. In every transaction with other members of society, brahmanas are certainly dependable. In this age, however, one must take into account that the brahmanas are uncertain in their qualifications. Because there are no yajñic brahmanas, all yajñas are forbidden. The only yajña recommended in this age is sankirtana-yajña. Yajñaih sankirtana-prayair yajanti hi sumedhasah (Bhag. 11.5.32). Yajña is meant to satisfy Visnu (yajñarthat karmano ’nyatra loko ’yam karma-bandhanah). Because in this age there are no qualified brahmanas, people should perform yajña by chanting the Hare Krsna mantra (yajñaih sankirtana-prayair yajanti hi sumedhasah). Life is meant for yajña, and yajña is performed by the chanting of Hare Krsna, Hare Krsna, Krsna Krsna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare.
Srimad Bhagavatam Canto 10, Chapter 07, Text 16
Srimad Bhagavatam Canto 10, Chapter 07, Text 18