[creating of evil] causes.
—Buddhist Saying (Part 1)
According to the ‘Sūtra On Arising Of Practices’《兴起行经》, in a distant past life, when Pípóyè Thus Come One (毘婆叶如来) was in Pántóumóbá city (槃头摩跋城) with 168,000 Great Bhikṣus (大比丘), Śākyamuni Buddha-to-be was the Brahmin (婆罗门) Yīntíqílì (因提耆利) then, the teacher of five hundred young disciples. One day, King Pántóu (槃头) invited the Buddha and his monastics for alms food in his palace. There, the Buddha requested for some food to take back for a sick monk named Maitreya (弥勒) (who later became Maitreya Bodhisattva [弥勒菩萨]), who could not join them.
When the Brahmin smelt the delicious food as they passed by, he became jealous and thought, ‘These Śramaṇas (沙门) with shaven heads should rightly eat horse wheat [i.e. oats], and should not eat this offering of tasty food.’ (此髠头沙门，正应食马麦，不应食此甘馔之供。) He said to his disciples, ‘You and others, do you see these practitioners with shaven heads, who ate tasty food or not?’ (汝等见此髠头道人，食于甘美肴膳不？) To which they all replied, ‘Thus truly as seen. These others, and their teacher, likewise should eat horse wheat.’ (尔实见。此等师主，亦应食马麦。) As a negative karmic result of having such jealousy and ill will towards the enlightened, as expressed in thought and speech, the Brahmin and his disciples passed through hell for innumerable thousands of years.
After the Brahmin became Śākyamuni Buddha (释迦牟尼佛), he was once, with these five hundred disciples reborn, who are now Arhats (阿罗汉), at Anavatapta (阿耨大泉) to enter the rains retreat. They were invited by the Brahmin Agnidattā (阿只达), who was supposed to offer them alms food throughout. However, he was confused by Māra (魔罗) to indulge in sense pleasures behind closed doors, while rejecting all visitors. As there was shortage of food due to famine, it was impossible to seek alms elsewhere.
When a horse breeder came to know this, he offered to share his horse wheat with them for 90 days (over three months). With nothing else to eat but this coarse food, this was the negative karmic effect of their past created evil. As the Brahmin in the past did not think or say that the Buddha should eat horse wheat, (as Buddhas are not shaven bald, but with remaining hair that never grow longer); only saying that the monks (Śramaṇas) should, the Buddha now ate naturally dehulled wheat kernel. As the disciples in the past thought and said that the Buddha should also eat horse wheat, thus having created more negative karma, the Arhats now ate wheat covered with hull.
Such was retribution from their collective karma (共业) and different karma (别业), with similar yet dissimilar effects, despite being already enlightened, albeit to different extents. Of course, the Buddha, being fully enlightened with all-knowing wisdom (一切智), should know how to not give supporting conditions (助缘) for each negative karmic seed to ripen. However, he should had chosen to undergo this incident to illustrate the certain and enduring nature of karma, as a cautionary example and reminder, for all to be mindful of their thoughts, words and deeds in terms of morality. If karma operates in such an exacting manner, even for the perfectly purified Buddha, it surely works likewise for the ignorant and unenlightened like us.
Sentient beings fear
[receiving of evil] effects.
— Buddhist Saying (Part 2)
Śūraṅgama Sūtra’s Section On Four Kinds Of Clear Instructions On Purity: Third Heavy Precept