来书云：「佛氏于『不思善，不思恶时，认本来面目』，于吾儒『随物而格』之功不同。吾若于不思善、不思恶时，用致知之功，则已涉于思善矣。欲善恶不思，而心之良知清静自在，惟有寐而方醒之时耳。斯正孟子『夜气』之说。但于斯光景不能久，倏忽之际，思虑已生，不知用功久者，其常寐初醒而思未起之时否乎？今澄欲求宁静，愈不宁静，欲念无生，则念愈生。如之何而能使此心前念易减，后念不生，良知独显，而与造物者游乎？」
「不思善、不思恶时，认本来面目。」此佛氏为未识本来面目者设此方便。本来面目则吾圣门所谓良知，今既认得良知明白，即已不消如此说矣。
「随物而格」是致知之功，即佛氏之「常惺惺」，亦是常存他本来面目耳。体段工夫大略相似，但佛氏有个自私自利之心，所以便有不同耳。今欲善恶不思，而心之良知清静自在，此便有自私自利、将迎意必之心，所以有「不思善、不思恶时，用致知之功，则已涉于思善」之患。孟子说「夜气」，亦只是为失其良心之人指出个良心萌动处，使他从此培养将去。今已知得良知明白，常用致知之功，即已不消说「夜气」。却是得兔后不知守兔，而仍去守株，兔将复先之矣。欲求宁静，欲念无生，此正是自私自利、将迎意必之病，是以念愈生而愈不宁静。良知只是一个良知，而善恶自辨，更有何善何恶可思！良知之体本自宁静，今却又添一个求宁静；本自生生，今却又添一个欲无生，非独圣门致知之功不如此，虽佛氏之学亦未如此将迎意必也。只是一念良知，彻头彻尾，无始无终，即是前念不灭，后念不生。今却欲前念易灭，而后念不生，是佛氏所谓断灭种性，入于槁木死灰之谓矣。
来信说：「佛家讲『不思善不思恶时，认本来面目』，与我们儒家『随物而格』的功夫不同。我若在不思善不思恶时用致知的功夫，就已涉于思善了。要善恶不思而心的良知清静自在，只有刚睡醒的时候。这正是孟子『夜气』之说。但这种光景不能持久，倏忽之间思虑已生。不知用功久的人，是否常在这种初醒思虑未起之时？如今我想求宁静，越发不宁静；想念头不生，念头越发丛生。怎样才能使此心前念易灭、后念不生，良知独显，而与造物者同游呢？」
「不思善不思恶时认本来面目」，这是佛家为不认识本来面目的人设的方便。本来面目就是我们圣门所谓的良知，如今既已认得良知明白，就不须再这样说了。
「随物而格」是致知的功夫，就是佛家的「常惺惺」，也就是常存他的本来面目罢了。体段功夫大略相似，但佛家有个自私自利之心，所以便有不同。如今想善恶都不思而心的良知清静自在，这便有自私自利、将迎意必之心，所以有「不思善不思恶时用致知之功，便已涉于思善」的毛病。孟子讲「夜气」，也只是为丢失了良心的人指出个良心萌动的地方，让他从这里培养下去。如今已认得良知明白，常用致知的功夫，就已不须再说「夜气」。这是得了兔子却不知道守着兔子，仍然去守树桩，兔子要再跑掉了。求宁静、求念头无生，这正是自私自利、将迎意必的病，所以念头越生而越发不宁静。良知只是一个良知，而善恶自辨，还有什么善什么恶可思！良知之体本自宁静，如今却又添一个求宁静；本自生生，如今却又添一个欲无生。不但圣门致知的功夫不如此，就是佛家之学也没有这样将迎意必的。只是一念良知，彻头彻尾，无始无终，就是前念不灭、后念不生。如今却想前念易灭、后念不生，这就是佛家所谓「断灭种性」，落入槁木死灰了。
Your letter says: 'The Buddhists say: not thinking good, not thinking evil, know the original face — differing from our Confucian work of following things and correcting. If at the time of not-thinking-good-and-evil I apply the work of extension, I am already involved in thinking good. For good and evil unthought and innate knowledge clear and at ease, there is only the moment of waking from sleep — Mencius's night breath. But the scene does not last; in a flash thought is born. Do veterans of the work abide in that first waking, thought not yet risen? Now I seek stillness and grow less still; seek thoughts unborn and they teem the more. How make the former thoughts die easily, the later not arise, innate knowledge alone shining, roaming companion to the Creator?'
Not-thinking-good-and-evil to know the original face is the Buddhists' expedient for those who do not know their original face. The original face is what our school calls innate knowledge: once innate knowledge is clearly known, such talk is spent.
Following things and correcting is the work of extension — the Buddhists' ever-alert, ever-preserving their original face. The frame of the work is much alike; but the Buddhists carry a self-serving heart, and there lies the difference. To will good-and-evil unthought while innate knowledge rests clear is itself the self-serving, forestalling, presuming heart — hence the trouble that applying extension already thinks good. Mencius's night breath only pointed, for those who had lost the good mind, to where it stirs, that they might nurture it from there. Now that innate knowledge is clearly known and the work of extension constantly applied, night breath need no longer be spoken. It is having caught the hare yet leaving it to guard the stump — the hare will bolt again. Seeking stillness, seeking thoughts unborn: that very seeking is the disease of self-serving and presumption, hence thoughts teem the more and stillness recedes. Innate knowledge is one innate knowledge, itself discerning good and evil — what good and evil remain to think? Its substance is still of itself, and you add a seeking of stillness; quick with life of itself, and you add a willing of no-life. Not only does the school's work of extension not do so — even the Buddhists do not thus forestall and presume. One thought of innate knowledge, head to tail, without beginning or end, is former thoughts undying and later thoughts unborn. To will former thoughts easily dead and later unborn is the Buddhists' extinct seed-nature, withered wood and cold ashes.