SB 12.6.44
tenasau caturo vedams
caturbhir vadanair vibhuh
sa-vyahrtikan somkarams
catur-hotra-vivaksaya
Translation:
All-powerful Brahma made use of this collection of sounds to produce from his four faces the four Vedas, which appeared together with the sacred omkara and the seven vyahrti invocations. His intention was to propagate the process of Vedic sacrifice according to the different functions performed by the priests of each of the four Vedas.