All of the Buddhist sutras that exist today came about after Buddha’s passing into nirvana. The earliest written recordings of his teachings are similar to the sutta, teachings in Pali held by the Hinayana vehicle. Typically, Hinayana practitioners only accept the sutta as Buddha’s teachings and reject all the sutras of the Mahayana and Vajrayana vehicles.

• The Hinayana or small vehicle teaches that life is fundamentally suffering and the best thing one can do to help others is to escape Samsara as an Arhat
• The Mahayana or big vehicle share the view that life is fundamentally suffering and that we must escape but extends this by taking the view that one should help as many others as possible to also become free from the suffering of cyclic existence
• The Vajrayana or diamond vehicle accepts the views of both the other systems and uses transformative techniques to develop the power to help self and others become lastingly free of suffering 

Fundamentally the variety of systems taught by Buddha express his desire to help all sentient beings by giving them different means to reach liberation according to their spiritual inclinations so that no one would be left behind without a means of escaping the sufferings of cyclic existence. All are valid and excellent but because their methods vary widely, not all teachings are compatible with each, hence Hinayana’s rejection of the texts from the other two vehicles. 

The Mahayana sutras were all transmitted subsequent to Buddha’s passing, some by writing down the oral tradition of preserving his words, others by spiritual transmission to great masters who had attained purity. However, there are some exceptions such as the High King Sutra, which was transmitted to a death row prisoner in a dream. Typically Mahayana practitioners accept the Mahayana sutras, and many also take the Hinayana suttas as teachings of the Buddha. However they may reject the sutras of Vajrayana, often because Shakyamuni didn’t speak them, although there are exceptions like the Heart Sutra.

Vajrayana has an even wider range of sutras including teachings not known or used by Hinayana or Mahayana practitioners, such as The Sutra on Entering the Womb. This sutra teaches how a master can direct his spirit upon his death, so as to reincarnate in a specific place, right down to which family. With this, he is able to leave instructions on where he can be found and how he can be identified. Thus we have the 14th Dalai Lama because the original Dalai Lama died and has come back 13 times to continue to lead his flock towards liberation.

Vajrayana typically accepts the Hinayana suttas and Mahayana sutras as the teachings of the Buddha but also asserts that since many others have attained Buddhahood since Buddha’s time, the teachings of these great saints and yogis are also deemed sutras – the teaching of a buddha.

Further, because Tantric practices take their lineage from Vairochana Buddha rather than from Shakyamuni, there are also sutras from deities other than Shakyamuni, such as Vairochana Buddha. Vajrayana is considered the school of mantras so most of the sutras containing mantra or dharani originate from it. However a number of these sutras are popular within Mahayana, such as the sutras spoken by Buddha which introduce the Great Compassion Dharani, the Dharani of Usnisavijaya Buddha Mother and the Dharani of Cundi Buddha Mother. In Vajrayana, these are considered part of “action tantra”.

This is a brief explanation but we can see that as we move through the three vehicles, the definition of a sutra broadens, with Vajrayana accepting the most comprehensive range of scriptures as sutras whilst Hinayana has the most specific definition.