The tradition's own origin story for the Abhidhamma is the most elaborate of the three baskets': it holds that the Buddha ascended to a heavenly realm to teach its content to his mother, reborn there, over the course of a single rains retreat, then descended and transmitted a summary to his disciple Sariputta, who worked it into the structured form now studied. Modern textual scholarship reads the material differently. Its systematic, technically precise style, its use of vocabulary and categories that develop and standardize gradually across its seven books, and its relatively late attestation compared with core sutta material together point most scholars toward regarding the Abhidhamma as a genuinely later layer of the canon, composed and elaborated by named and unnamed scholar-monks over some centuries after the Buddha's death rather than delivered whole in a single teaching episode.
That scholarly reading does not diminish the basket's standing within the tradition, where it is treated as the fullest and most precise statement of the teaching's underlying structure, closer to its ultimate truth than the more accessible narrative teaching in the Sutta Pitaka. Different early Buddhist schools produced their own, non-identical Abhidhamma collections, and the seven-book version preserved in Pali is the one that became the Theravada school's canonical Abhidhamma specifically, distinct from parallel Abhidharma literature preserved by other early schools in Sanskrit and Chinese transmission.