"Just as a chariot with one wheel Will not go down the path even though it has a horse,
So too, without assistants for meditation,
People will not gain attainments.
These assistants should have intelligence, a good appearance, great purity,
Be of reputable lineage, and inclined toward the teachings.
They should have great confidence, perseverance, and have disciplined the senses.
They should speak pleasantly, be generous and compassionate,
Forbear hunger, thirst, and the afflictions,
And not worship other deities and brahmins.
They should be focused, adept, grateful,
And have faith in the three jewels.
Since those who have all such good qualities
Are very rare in this age of strife,
Mantra practitioners should rely on an assistant who has
One half, one quarter, or an eighth of these qualities."

Subāhu-pariprcchā-tantra