A basic Buddhist writ.
The Pali Canon contains a collection of sutras (called sutta in Pali), which record various sayings of the Buddha.
Most of the Pali sutras/suttas start with the words "Thus have I heard." This is because all of them were originally traded as part of an oral tradition. To ensure the texts would not be changed over a period of time, monks of the Southern Buddhist tradition used to memorize them, then recite them outloud every day. If one monk forgot a word or two, another monk could correct him.
Eventually, the monks gathered at the Buddhist Council in Ceylon decided to write the texts down. They wrote them down in the Pali language, hence the name Pali Canon.
Mahayana Buddhism contains a wealth of other sutras, not necessarily dating back all the way to the days of the Buddha. Some describe acts of other noted Buddhists of the Mahayana tradition, and offer additional insights into dharma.
Note: I am only describing Buddhist sutras here. This is not to imply than the word sutra only pertains to Buddhism. As the Webster definition shows, Hindu tradition also has sutras. But I do not know enough about them to talk about them. Maybe someone else can...