佛祖統紀 3.78

3.78

第二鹿苑時者。佛本以大乘擬度眾生。其不堪者。尋思方便趣波羅柰（此云江遶城。中印度境。鹿苑在城中）於一乘道分別說三。即是開三藏教也。非但釋迦隱其無量神德作斯漸化。去來諸佛亦復如是。當知初頓之後次開於漸。漸機於頓全生如乳。三藏中轉革凡成聖。喻變乳為酪。次第相生不取濃淡（妙玄十）為三乘根性於頓無益故。不動寂場而遊鹿苑。脫舍那珍御之服。著丈六弊垢之衣。先為五人說四諦十二因緣事六度等教（四教儀○文句云。過去名根。未來名性○即大而小。故云不動。尊特勝應定慧莊嚴。譬珍御服。生身劣應忍生法惱。譬以垢衣。佛生人中。倍勝人形。故長丈六。如彌勒三十二丈時人長十六丈）。

Regarding the second period, the Deer Park period: The Buddha originally intended to deliver sentient beings with the Mahāyāna, but for those who were incapable of it, he devised expedient means and proceeded to Vārāṇasī (translated here as "river-encircled city," a territory of central India; the Deer Park is within the city), and within the One Vehicle path he distinctively expounded three, which was the opening of the Tripiṭaka teaching. Not only did Śākyamuni conceal his immeasurable divine virtues to carry out this gradual transformation; the Buddhas of the past and future do likewise. One should know that after the initial sudden, the gradual was subsequently opened. The faculties suited for the gradual were, in relation to the sudden, entirely raw like fresh milk; within the Tripiṭaka they were transformed from ordinary beings into sages, likened to changing milk into curds, each arising sequentially without regard to rich or thin (Miao xuan, fascicle 10). Because for those of the three vehicles' faculties and nature there was no benefit in the sudden, without moving from the tranquil bodhimaṇḍa he journeyed to the Deer Park, took off the precious royal robe of Rocana, put on the worn, soiled garments of the sixteen-foot body, and first expounded for the five men the teachings of the Four Truths, Twelvefold Dependent Origination, and phenomenal six pāramitās (Sijiao yi. The Wenju states: "Past is called roots; future is called nature." Reaching the small from the great is why it says "without moving." The superior response of the exalted and distinctive [body], adorned with samādhi and wisdom, is likened to the precious royal robe; the inferior response of the birth-body, bearing the afflictions of beings and phenomena, is likened to the soiled garments. The Buddha was born among humans, twice the height of human stature, hence sixteen feet tall; just as when Maitreya is thirty-two fathoms tall, the people of that time will be sixteen fathoms).