The seventh sutta of the Cūḷa Vagga of the Suttanipāta.

Several old and decrepit but wealthy (Mahāsāla) brahmins of Kosala, visit the Buddha at Jetavana and ask him if the practices of the brahmins of their own day are in conformity with those of old. The Buddha answers in the negative and describes in detail the high moral standard of the lives of ancient brahmins. In course of time, however, the brahmins were disturbed by the sight of the king’s wealth and adorned and bejewelled women, and became covetous of these. They thereupon induced the king to make offerings and hold sacrifices of animals that these might be for their own gain. Thus righteousness decayed and disease became prevalent among men.

The brahmins, pleased with the Buddha’s discourse, declared themselves his followers. SN.pp.50-55.