Probably refers to Āsīvisa Sutta (S.iv.172), but may be (2).

It was taught by Majjhantika Thera to the Nāga-king Aravāla and the people of Kasmīra and Gandhāra.

Eighty thousand of the listeners accepted the new religion and one hundred thousand were ordained after the discourse (Sp.i.66; Mhv.xii.26).

It was also taught by Mahinda in Sri Lanka in the Nandanavana at Anurādhapura on the third day after his entry into the city. Thirty thousand people were converted. Ibid., xv.178-9; Sp.i.80; Mbv.133.