The Three Jewels ( Skt. Triratna, also: Three Jewels, Triple Gems, Three Treasures ) call in Buddhism Buddha, Dharma ( the Buddha teachings) and Sangha (this is depending on the school differently, usually meant only the community of the Awakened in some schools, but also the general Sangha, which includes practitioners in their entirety). They are the objects of the triple refuge for Buddhists. Only by taking refuge in the Three Jewels, and that from the deepest inner conviction, someone is considered to be a Buddhist.
The traditional formula in Pali is:
Buddham Saranam Saranam gacchami Dhammam gacchami Sangham Saranam gacchami.
I take refuge in the Buddha I take refuge in the Dharma I take refuge in the Sangha.
It is spoken three times in succession, as in ancient India as a sign of complete conviction was the custom.
At the ceremony, the first refuge to the community, the practitioners also the five Silas committed mostly, to observe the moral rules of the Buddhists.
In Mahayana Buddhism Uttara Tantra Shastra the work ( rgyud bla ma) of Maitreya / Asanga is considered the seminal work in the Three Jewels.