Brihadaranyaka-Upanishad: Fifth Adhyâya, Eighth Brahmana

1. Let him meditate on speech as a cow. Her four udders are the words Svaha, Vashat, Hanta, and Svadha. The gods live on two of her udders, the svaha and the Vashat, men on the Hanta, the fathers on the Svadha. The bull of that cow is breath (prâna), the calf the rnind.