The Cambridge History of India, Vol. I: Ancient India v1.c17.133

v1.c17.133

but they insist that there shall be no marriage with agnates or cognates, and they require that a man must either marry in his own caste, or if he marries out of his caste, it must be into a lower caste. But while some authorities so lay down this rule as to allow the Brāhman to marry into the next two lower castes, the Kshatriya and the Vaiçya, and the Kshatriya to marry into the Vaiçya caste, others also permit marriage with Çūdrās, and therefore allow a Vaiçya to marry into that caste.