SB 12.6.61
vaisampayana-sisya vai
carakadhvaryavo ’bhavan
yac cerur brahma-hatyamhah
ksapanam sva-guror vratam
Translation:
The disciples of Vaisampayana became authorities in the Atharva Veda. They were known as the Carakas because they executed strict vows to free their guru from his sin of killing a brahmana.