佛祖統紀 34.40

34.40

With respect to nirvāṇa, there are two meanings: First, for those whose faculties were not yet ripe during the Lotus, he retroactively preached the four teachings and fully discussed the Buddha-nature, enabling them to know the true eternal and enter the great nirvāṇa; this is called the teaching of gathering up the remaining faculties. Second, because people of later ages would lose both the vehicle and the precepts, he further supported the Tripiṭaka and broadly opened the doctrine of eternity, setting up three kinds of expedients to support the one perfect reality; this is called the teaching of supporting the vinaya and discussing the eternal. If discussed in terms of time and flavor, it is identical with the Lotus (Nirvāṇa was preached when on the verge of extinction. From the previous passage, 'After realizing the Way, the Tathāgata turned the wheel of the true Dharma' downward, see the detailed account in the Basic Annals of the Buddha).