The teachings of the Buddha have been preserved in the Tipitaka. The Pali word, 'Tipitaka', literally means 'the three baskets' (ti- three + pitaka- basket). All of the Buddha's teachings were divided into three parts.
The first part is known as the Suttanta Pitaka and it contains the Discourses.
The second part is called the Vinaya Pitaka and it contains all the rules the Buddha laid down for monks and nuns.
The third part is known as the Abhidhamma Pitaka and comprises the Buddha's teachings on his psycho-ethical philosophy.
Whenever the Buddha gave a discourse to his ordained disciples or lay-followers, or prescribed a monastic rule in the course of his forty-five year ministry, those of his devoted and learned monks then present would immediately commit his teachings word for word to memory.
Thus the Buddha's
words were preserved and were passed down
orally from teacher to pupil.