法華義疏 1.140

1.140

〈壽量品〉云「如來如實知見三界之相，無有生死若退若出。又無在世及滅度者，非實非虛非如非異」，六無四非即其事也。外國名佛以為天鼓，賊欲來時天鼓則鳴，賊欲去時天鼓亦鳴，天鼓鳴時諸天心勇，天鼓鳴時修羅懼怖，眾生煩惱應來佛則為說法，眾生煩惱應去佛則為說法，佛說法時弟子心勇，佛說法時諸魔懼怖，天鼓無心能為四事，如來雖說亦復無心，是故詺佛以為天鼓也。又如來雖覺實無所悟，喻天鼓雖鳴實無心也。

The "Lifespan Chapter" says: "The Tathāgata knows and sees the characteristics of the three realms as they truly are: there is no birth and death, whether regressing or emerging; there is also neither remaining in the world nor entering extinction; neither real nor unreal, neither thus nor different." The six negations and four exclusions are precisely this matter.
In foreign countries, the Buddha is called a celestial drum. When bandits are about to come, the celestial drum sounds; when bandits are about to leave, the celestial drum also sounds. When the celestial drum sounds, the hearts of the devas become courageous; when the celestial drum sounds, the asuras become frightened. When the defilements of sentient beings are due to arise, the Buddha preaches the Dharma for them; when the defilements of sentient beings are due to cease, the Buddha preaches the Dharma for them. When the Buddha preaches the Dharma, the hearts of the disciples become courageous; when the Buddha preaches the Dharma, the māras become frightened. The celestial drum has no mind yet can perform these four functions; although the Tathāgata preaches, he also has no mind. Therefore the Buddha is called a celestial drum. Furthermore, although the Tathāgata is enlightened, in reality there is nothing awakened to, just as the celestial drum sounds yet in reality has no mind.