Buddhaghosa's commentary on the Dhammasanganippakarana of the Abhidhamma Pitaka.
It was originally written in India (Mhv.xxxvi.225; Sas.31), but was probably revised in Ceylon as it mentions (pp. 97-8) the Samantapásádiká, also various Atthakathás and the Visuddhi Magga.