The Dalai Lama's Heart of Wisdom Teachings, Wisdom Publications (2005), p.54

"It is very important to understand that the core teachings of the Theravada tradition embodied in the Pali scriptures are the foundation of the Buddha's teachings. Beginning with these teachings, one can then draw on the insights contained in the detailed explanations of the Sanskrit Mahayana tradition. Finally, integrating techniques and perspectives from the Vajrayana texts can further enhance one's understanding. But without a foundation in the core teachings embodied in the Pali tradition, simply proclaiming oneself a follower of the Mahayana tradition is meaningless."

~ Dalai Lama, Essence of the Heart Sutra