The 9 Vehicles of Nyingma Tradition By Alak Zenkar Rinpoche
Our teacher, the fourth guide of this fortunate eon, the incomparable lord of sages, Sakyamuni, gave infinite teachings as means to enter the Dharma of the causal and resultant vehicles, in accordance with the particular temperaments, spiritual faculties, and attitudes of disciples. Nevertheless, they may all be included within the three vehicles, which, in turn, may be further subdivided into nine successive stages.
The General Sutra says:
The ultimate definitive vehicle
Certainly appears as three in number:
The .