Abhidhamma
The following extract is taken from The Expositor (Atthasālinī), which is the primary commentary on the Dhammasaṅgaṇī (the first book of the Abhidhamma). It describes the lineage of the Abhidhamma and the pivotal role of Ven. Sāriputta in organizing the teachings for human study.
> The Origin and Transmission of the Abhidhamma
Sāriputta, generalissimo of the Law, went there, served the Supreme Buddha, and sat aside. Then to him the Teacher gave the method, saying: “Sāriputta, 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.
The Five Hundred Bhikkhus and the Bats
Now Sāriputta, having learned the law taught by the Teacher, preached it to five hundred bhikkhus, his own pupils. The following is their connection with the past:
They, so it is said, were born as bats in the time of the Buddha Kassapa.
Hanging from the roof of a cave, they heard the voice of two bhikkhus reciting the Abhidhamma and grasped a general idea that it was the Law, though they were unable to distinguish the good from the bad.
They passed away with only the general idea suggested by the voice and were reborn in the world of gods.
They dwelt there during a whole interval between the death of one Buddha and the appearance of the next, and in the time of this Buddha were reborn as men.
Being convinced by the Twin Miracle, they renounced the world in the presence of the Elder who, having learned the Law taught by the Teacher, preached it to them. Their acquirement of the seven books was simultaneous with the conclusion of the Abhidhamma teaching of the Buddha.
The Role of Sāriputta
The textual order of the Abhidhamma originated with Sāriputta; the numerical series in the Great Book (Paṭṭhāna) was also determined by him. In this way the Elder, without spoiling the unique doctrine, laid down the numerical series in order to make it easy to learn, remember, study, and teach the Law.
Such being the case, was the Elder the very first to understand the Abhidhamma? Nay, it was the Supreme Buddha who first understood the Abhidhamma. For he, seated on the throne under the Wisdom Tree, penetrated it and became the Buddha and, while seated for seven days in one position on the throne, uttered this song of ecstasy:
"Lo! when appear true doctrines to the saint
Zealous and thoughtful, all his doubts dissolve;
He knows that all Becoming is through Cause.
Lo! when appear true doctrines to the saint
Zealous and thoughtful, all his doubts dissolve;
He knows the demolition of all Cause."The Expositor (Atthasālinī): Buddhist Psychological Ethics. (Maung Tin, Trans.; C.A.F. Rhys Davids, Ed.). London: Published for the Pali Text Society by Oxford University Press. (Original work published 5th century C.E.), pp. 16–17.