An arahant. He was born in Vesāli, and was one of those who heard the Buddha preach when he came to quieten the panic which arose there, as recorded in the Ratana Sutta (q.v.). After the sermon Kosalavihārī left the world. At the conclusion of his novitiate he dwelt in a forest near a village in Kosala. A lay adherent seeing him camping under a tree built for him a small hut, and there the thera attained arahantship. He acquired his name from having dwelt long in Kosala (Thag.59; ThagA.i.134f).
In the time of Padumuttara Buddha he was an ascetic in Himavā and gave the Buddha some tuberous roots. Fifty-four kappas ago he was a king named Sumekhalisama. He is evidently to be identified with Bilālidāyaka of the Apadāna. Ap.i.145.