"Two monks, Brahmans by birth, were troubled that other monks of various clans, tribes, and families, were corrupting the Buddha's words by repeating them each in his own dialect (sakāya niruttiyā).
They asked the Buddha, 'Let us put the Buddha's words into Vedic Sanskrit verse (chandaso āropema).' But the Blessed One, the Buddha, rebuked them...
And he commanded the monks: 'You are not to put the Buddha's words into Vedic Sanskrit verse. To do this would be to commit an infraction. I authorize you, monks, to learn the Buddha's words each in his own dialect.'"
Vinayapitaka 2:139, translation available in Pollock, Sheldon: The Language of the Gods in the World of Men: Sanskrit, Culture, and Power, p. 54