大方便佛報恩經 6.103

6.103

答曰：「齋法過中不食為體，八事助成齋體，共相支持，名八支齋法，是故言八齋，不云九也。」

[The Buddha] replied: "The observance has not eating past noon as its substance; the eight items assist in completing the substance of the observance, mutually supporting each other, and are called the eightfold observance. Therefore it is called the eightfold observance, not nine."