The Bodhisatta was once an ascetic of great power. The king of Benares, having heard at night four sounds - du, sa, na, so - uttered by four beings who dwelt in hell, was greatly frightened. When he consulted his purohita, the latter ordained a fourfold sacrifice. The Bodhisatta, seeing the fate that lay in wait for numerous creatures, went to the king's park and there, with the help of the purohita's chief disciple - not himself in favour of the sacrifice - explained to the king the meaning of the sounds and had the sacrificial animals released. The purohita's disciple is identified with Sāriputta.
The story was told in reference to Pasenadi, who one night heard four syllables uttered by four inhabitants of hell. These had once been nobles of Sāvatthi, guilty of adultery. After death they were born in four iron cauldrons. After sixty thousand years they had gradually come to the top of these cauldrons and had uttered these syllables in their attempt to proclaim their misery. The king, very frightened, consulted his priests, who ordered a sacrifice. But Mallikā intervened and sent the king to see the Buddha, who explained the matter and allayed the king's fears.
J.iii.43 8; the stories, both of the past and present, appear also at DhA.ii.5ff. and PvA.279ff. In both places the introductory story gives greater details. Pasenadi heard the sounds while lying sleepless, because he contemplated putting a helpless man to death in order to obtain his beautiful wife. There are also other differences in the two accounts. For details see Burlinghame: Buddhist Legends ii.100, n.1.