Mandukya Karika, verse 4.86
Text
विप्राणां विनयो ह्येष शमः प्राकृत उच्यते ।
दमः प्रकृतिदान्तत्वादेवं विद्वाञ्शमं व्रजेत् ॥ ८६ ॥
viprāṇāṃ vinayo hyeṣa śamaḥ prākṛta ucyate |
damaḥ prakṛtidāntatvādevaṃ vidvāñśamaṃ vrajet || 86 ||
86. This (i.e., the realisation of Brahman) is the humility natural to the Brāhmaṇas. Their tranquillity (of mind) is also declared to be spontaneous (by men of discrimination). They are said to have attained to the state of sense-control (not through any artificial method as it comes quite natural to them. He who thus realises Brahman which is all-peace, himself becomes peaceful and tranquil.
Shankara Bhashya (commentary)
The humility of the Brāhmaṇas which is due to their realisation of their identity with the Self, is quite natural. This is (the real significance of) his humility. The tranquillity (of the mind which the Knowers of Brahman enjoy) is also natural and not induced by any artificial1 means. Brahman is all peace and tranquility. Hence the Brāhmaṇas are said to have controlled their sense-organs (from pursuing the external objects). This is also the cause of the tranquillity of their nature. Having realised Brahman which is, by nature, all-peace the wise man attains to peace which is the characteristic of Brahman. That is to say, he becomes identical with Brahman.