Hi all, this part of the introduction to CMA by Bhikkhu Bodhi seems most relevant to our discussion, so I'll reproduce it here together with the first paragraph that Ben transcribed earlier so that people don't need to search for it on the previous page.
The Origins of the Abhidhamma
Although modern critical scholarship attempts to explain the formation of the Abhidhamma by a gradual evolutionary process,4 Theravada orthodoxy assigns its genesis to the Buddha himself. According to the Great Commentary (maha-atthakatha) quoted by Acariya Buddhaghosa, "What is known as Abhidhamma is not the province nor the sphere of a disciple; it is the province, the sphere of the Buddhas."5 The commentarial tradition holds, moreover, that it was not merely the spirit of the Abhidhamma, but the letter as well, that was already realized and expounded by the Buddha during his lifetime.
The Atthasalini relates that in the fourth week after the Enlightenment, while the Blessed One was still dwelling in the vicinity of the Bodhi Tree, he sat in a jewel house (ratanaghara) in the northwest direction. This jewel house was not literally a house made of precious stones, but was the place where he contemplated the seven books of the Abhidhamma Pitaka. He contemplated their contents in turn, beginning with the Dhammasangani, but while investigating the first six books his body did not emit rays. However, upon coming to the Patthana, when "he began to contemplate the twenty-four universal conditional relations of root, object, and so on, his omniscience certainly found its opportunity therein. For as the great fish Timiratipingala finds room only in the great ocean 84,000 yojanas in depth, so his omniscience truly finds room only in the Great Book. Rays of six colors — indigo, golden, red, white, tawny, and dazzling — issued from the Teacher's body, as he was contemplating the subtle and abstruse Dhamma by his omniscience which had found such opportunity."6
Theravada orthodoxy thus maintains that the Abhidhamma Pitaka is authentic Word of the Buddha, in this respect differing from an early rival school, the Sarvastivadins. This school also had an Abhidhamma Pitaka consisting of seven books, considerably different in detail from the Theravada treatises. According to the Sarvastivadins, the books of the Abhidhamma Pitaka were composed by Buddhist disciples, several being attributed to authors who appeared generations after the Buddha. The Theravada school, however, holds that the Blessed One himself expounded the books of the Abhidhamma, except for the detailed refutation of deviant views in the Kathavatthu, which was the work of the Elder Moggaliputta Tissa during the reign of Emperor Asoka.
The Pali Commentaries, apparently drawing upon an old oral tradition, maintain that the Buddha expounded the Abhidhamma, not in the human world to his human disciples, but to the assembly of devas or gods in the Tavatimsa heaven. According to this tradition, just prior to his seventh annual rains retreat the Blessed One ascended to the Tavatimsa heaven and there, seated on the Pandukambala stone at the foot of the Paricchattaka tree, for the three months of the rains he taught the Abhidhamma to the devas who had assembled from the ten thousand world-systems. He made the chief recipient of the teaching his mother, Mahamaya-devi, who had been reborn as a deva. The reason the Buddha taught the Abhidhamma in the deva world rather than in the human realm, it is said, is because in order to give a complete picture of the Abhidhamma it has to be expounded from the beginning to the end to the same audience in a single session. Since the full exposition of the Abhidhamma requires three months, only devas and Brahmas could receive it in unbroken continuity, for they alone are capable of remaining in one posture for such a length of time.
However, each day, to sustain his body, the Buddha would descend to the human world to go on almsround in the northern region of Uttarakuru. After collecting almsfood he went to the shore of Anotatta Lake to partake of his meal. The Elder Sariputta, the General of the Dhamma, would meet the Buddha there and receive a synopsis of the teaching given that day in the deva world: "Then to him the Teacher gave the method, saying, 'Sariputta, so much doctrine has been shown.' Thus the giving of the method was to the chief disciple, who was endowed with analytical knowledge, as though the Buddha stood on the edge of the shore and pointed out the ocean with his open hand. To the Elder also the doctrine taught by the Blessed One in hundreds and thousands of methods became very clear."7
Having learned the Dhamma taught him by the Blessed One, Sariputta in turn taught it to his own circle of 500 pupils, and thus the textual recension of the Abhidhamma Pitaka was established. To the Venerable Sariputta is ascribed the textual order of the Abhidhamma treatises as well as the numerical series in the Patthana. Perhaps we should see in these admissions of the Atthasalini an implicit acknowledgement that while the philosophical vision of the Abhidhamma and its basic architecture originate from the Buddha, the actual working out of the details, and perhaps even the prototypes of the texts themselves, are to be ascribed to the illustrious Chief Disciple and his entourage of students. In other early Buddhist schools, too, the Abhidhamma is closely connected with the Venerable Sariputta, who in some traditions is regarded as the literal author of Abhidhamma treatises.8
Notes:
4. See, for example, the following: A.K. Warder, Indian Buddhism, 2nd rev. ed. (Delhi: Motilal Banarsidass, 1980), pp. 218-24; Fumimaro Watanabe, Philosophy and its Development in the Nikayas and Abhidhamma (Delhi: Motilal Banarsidass, 1983), pp. 18-67; and the article "Abhidharma Literature" by Kogen Mizuno in Encyclopaedia of Buddhism, Fasc. 1 (Govt. of Ceylon, 1961).
5. Asl. 410; Expos., p. 519
6. Asl. 13; Expos., pp. 16-17
7. Asl. 16; Expos., p. 20
8. The first book of the Sarvastivadin Abhidharma, the Sangitiparyaya, is ascribed to Sariputta by Chinese sources (but not by Sanskrit and Tibetan sources), while the second book, the Dharmaskandha, is ascribed to him by Sanskrit and Tibetan sources (but not by Chinese sources). The Chinese canon also contains a work entitled the Shariputra Abhidharma-Shastra, the school of which is not known.