Srimad Bhagavatam Canto 02, Chapter 06, Text 25

SB 2.6.25

vastuny osadhayah sneha
rasa-loha-mrdo jalam
rco yajumsi samani
catur-hotram ca sattama
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Other requirements are utensils, grains, clarified butter, honey, gold, earth, water, the Rg Veda, Yajur Veda and Sama Veda and four priests to perform the sacrifice.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
To perform a sacrifice successfully, at least four expert priests are needed: one who can offer (hota), one who can chant (udgata), one who can kindle the sacrificial fire without the aid of separate fire (adhvaryu), and one who can supervise (brahma). Such sacrifices were conducted from the birth of Brahma, the first living creature, and were carried on till the reign of Maharaja Yudhisthira. But such expert brahmana priests are very rare in this age of corruption and quarrel, and therefore in the present age only the yajña of chanting the holy name of the Lord is recommended. The scriptures enjoin:
 
harer nama harer nama
 harer namaiva kevalam
kalau nasty eva nasty eva
 nasty eva gatir anyatha
Srimad Bhagavatam Canto 02, Chapter 06, Text 24
Srimad Bhagavatam Canto 02, Chapter 06, Text 26