Hi SDC, Abhidhamma Pitaka
The Basket of Abhidhammahttp://www.accesstoinsight.org/tipitaka/abhi/index.html
According to tradition, the essence of the Abhidhamma was formulated by the Buddha during the fourth week after his Enlightenment. Seven years later he is said to have spent three consecutive months preaching it in its entirety in one of the deva realms, before an audience of thousands of devas (including his late mother, the former Queen Maya), each day briefly commuting back to the human realm to convey to Ven. Sariputta the essence of what he had just taught. Sariputta mastered the Abhidhamma and codified it into roughly its present form. Although parts of the Abhidhamma were recited at the earlier Buddhist Councils, it wasn't until the Third Council (ca. 250 BCE) that it became fixed into its present form as the third and final Pitaka of the canon.
 Handbook of Pali Literature, by Somapala Jayawardhana (Colombo: Karunaratne, 1994), p. 1.
 From the Atthasalini, as described in Great Disciples of the Buddha, by Nyanaponika Thera and Hellmuth Hecker (Somerville: Wisdom Publications, 1997), pp. 45-46.
 The Katthavatthu, composed during the Third Council, was the final addition to the Abhidhamma Pitaka. See Guide Through the Abdhidhamma Pitaka, by Nyanatiloka Mahathera (Kandy: Buddhist Publication Society, 1983), p xi.