法苑珠林 33.53

33.53

如譬喻經云。佛以臘月八日神通降伏六師。六師不如投水而死。仍廣說法度諸外道。外道伏化白佛言。佛以法水洗我心垢。我今請僧洗浴以除身穢。仍為常緣也（今臘月八日洗僧唯出此經文）。

As the Dṛṣṭānta-sūtra says: On the eighth day of the twelfth month, the Buddha subdued the six non-Buddhist masters through supernormal powers. The six masters, unable to match him, threw themselves into the water and died. He then expounded the Dharma extensively to deliver the non-Buddhists. The non-Buddhists submitted, were transformed, and addressed the Buddha, saying, "The Buddha has washed away the defilements of our minds with the water of the Dharma. We now invite the monks to bathe in order to remove the impurities of their bodies." This subsequently became an ongoing regular practice (bathing the monks on the eighth day of the twelfth month appears only in this sūtra text).