As I discuss in this question, by far the most popular school of Hindu philosophy today is the Vedanta school, which is based on the philosophical portions of the Vedas. But in the time when Buddhism was at its peak popularity in India, the most popular school of Hindu philosophy was the Purva Mimamsa school, which was based on the ritualistic portions of the Vedas.
Now one of the most famous Purva Mimasa philosophers was named Kumarila Bhatta, and in this excerpt from his work the Tantra Vartika, he argues that Hindus should not accept Buddhist texts as valid scripture, because Buddha was a violator of the Vedas:
Then again, we find that the Bauddha teachings were given by one who was a born Kshatriya; and as such, he transgressed the duties of his own class, in taking upon himself the work of taking and receiving presents (which are the monopoly of the Brahmanas); and hence how can we believe that true Dharma or Duty would be taught by one who has transgressed his own Dharma? It has been well said: "One who is found to be doing deeds opposed to a prosperous hereafter, should be shunned from a distance; because how can one who deceives himself offer any salutary advice to others?"
Such transgression of Dharma by Buddha is clearly mentioned in the Alankarabuddhi (a Bauddha work), where Buddha is represented as saying - "May all the pain proceeding from the sins due to the Iron Age, rest in me, and leave humanity at large absolutely free!" And in connection with this his followers eulogise his virtues in the following strains: "For the sake of the well-being of humanity, He transgressed his own duties as a Kshatriya, and having taken up the duties of the Brahmana, he taught, even to the people outside the pale of Vedic religion, such truths relating to Dharma, as were not taught by Brahmanas who were unable to transgress the prohibition (of such teachings being imparted by outsiders); and thus prompted by his mercy to others, he even went to the length of transgressing his own Dharma!" And we actually find His followers behaving in a manner entirely at variance with the teachings of the Veda.
I found the quote in bold interesting, because it seems reminiscent of the Christian notion that "Jesus died for our sins". So my question is, does the Buddhist text that Kumarila Bhatta is quoting from, the Alankarabuddhi, still exist?
By the way, when the Alankarabiddhi quote says "Iron Age", that's an English translation of the Sanskrit term "Kali Yuga", which refers to the Hindu notion that we are currently living in an age of evil. Now I think only some sects of Buddhism share this Hindu belief, so that may help in finding this text.