The thirteenth sutta of the Digha Nikāya, preached to Vāsettha and Bhāradvāja who visited the Buddha at Manasākata.
The Buddha points out the futility of the belief that a mere knowledge of the Three Vedas leads to the attainment of reunion with Brahmā.
Such union can, however, be attained only by the practice of the four Brahma-vihāras. D.i.235-53.