大方廣佛華嚴經疏 50.28

50.28

第六「佛子譬如火大」下隨緣起盡，有喻、合、結。合中，以機喻薪、以涅槃喻火。眾生善根未熟，可熟者成正覺，以熟之如為火事。若所應度者皆已度竟，則現般涅槃寂無所為，如火息滅。故《法華》云「佛此夜滅度，如薪盡火滅。」然現滅現生，皆是涅槃大用，故《攝論》第十名「涅槃如火。」既起滅在緣，則益不可盈、損不可虧云云，自彼非佛然也。

Sixth, from "Bodhisattvas, like the fire element..." onward, arising and ending in accord with conditions, having a simile, application, and conclusion. In the application, the capacity [of beings] is compared to firewood, and nirvāṇa is compared to fire. When sentient beings' roots of goodness are not yet mature, for those who can be matured, he achieves sambodhi to mature them, just as fire performs its work. If those who should be saved have all been saved, he manifests parinirvāṇa, quiescent with nothing to do, just as fire goes out. Therefore, the Lotus Sūtra says: "The Buddha this night passes into extinction, like fire going out when firewood is exhausted." However, manifesting cessation and manifesting birth are both the great function of nirvāṇa; hence the tenth chapter of the Mahāyānasaṃgraha names it "nirvāṇa like fire." Since arising and cessation depend on conditions, then increase cannot make it wax, and decrease cannot make it wane, and so forth; it comes from them, not from the Buddha being so.