We come now to one of the most important contributions made by the Venerable Sariputta to Buddhist teaching. According to tradition (e.g., in the Atthasalini), the Buddha preached the Abhidhamma in the Tavatimsa heaven to his mother, Queen Maya, who had been reborn as deva in that world. He did this for three months, and when returning daily to earth for his meals, he gave to the Venerable Sariputta the "method" (naya) of that portion of Abhidhamma he had preached. The Atthasalini says; "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 the doctrine taught by the Blessed One in hundreds and thousands of methods became very clear." Thereafter, the Elder passed on what he had learned to his five hundred disciples.
Further it is said: "The textual order of the Abhidhamma originated with Sariputta; the numerical series in the Great Book (Patthana) 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."
...