佛祖統紀 3.103

3.103

The commentary says: The Tathāgata traveled through the sixteen great kingdoms during the twelve years delivering people, preaching the four Āgamas and other sūtras as well as the brief admonitions of the seven Buddhas. Only by this year did he begin to preach the expanded precepts, namely, the two hundred and fifty precepts for monks and the five hundred precepts for nuns. Because [transgressions arose among] the two assemblies, rules were instituted in response to offenses, and the Buddha later compiled these clauses and articles, making them the basis to be observed and revered by those who have left the household.