Samyukta Āgama (2) 46
The four guardian kings
At that time the World-honored One said to the monks: “On the eighth day of every fortnight the four guardian kings send out their messengers to walk the earth and observe who in the world practices filial piety, respects elders, makes offerings to renunciants and brāhmaṇas and does good, and who does evil. For this reason one should do good, get rid of all evil behavior, and keep the precepts.
Again on the fourteenth day of every fortnight the four guardian kings send out their sons to walk the earth; and on the fifteenth day of every fortnight the four guardian kings themselves walk the earth to observe in the same way.
Having observed human behavior, the four guardian kings ascend to see Sakka in the Hall of True Dhamma. They report to Sakka and the other Tāvatiṃsa devas: ‘In the world there are many human beings who do not observe filial piety, do not respect renunciants and brāhmaṇas, do not make offerings to their teachers and the clan elders, and so on…; and not many keep the precepts.’ When Sakka and the host of devas hear these words, they are sad and unhappy. The gods say: ‘The host of devas will decrease, and the host of asuras will grow.’
If, however, there are human beings in the world who always practice filial piety, make offerings to renunciants and brāhmaṇas, and so on …, and many who keep the precepts, then the four guardian kings go up and report this to Sakka. Then the devas are very much delighted and all say: ‘The human beings in the world are acting in a wholesome way. They are indeed wise and good and doing what they should do. The number of devas will grow, and the number of asuras will decrease.’
Sakka is pleased and speaks a verse:
“Those who on the eighth, the fourteenth /
and the fifteenth,
as well as during the fortnight when the spirits walk /
keep the precepts in purity –
they will be reborn in heaven, /
their merit equaling my own.’”