Verse 5.6

तिस्रो मात्रा मृअत्युमत्यः प्रयुक्ता अन्योन्यसक्ताः अनविप्रयुक्ताः ।
क्रियासु बाह्याभ्यन्तरमध्यमासु सम्यक्प्रयुक्तासु न कम्पते ज्ञः ॥ ७ ॥

tisro mātrā mṛatyumatyaḥ prayuktā anyonyasaktāḥ anaviprayuktāḥ |
kriyāsu bāhyābhyantaramadhyamāsu samyakprayuktāsu na kampate jñaḥ || 6 ||

6. When the three matras, each of which leads to death by itself, are joined one to another in close union and used in well-performed actions, external, internal and intermediate, the knower does not shake.

Shankara’s Commentary:

Com.—The matras of the syllable ‘Om’ three in number, i.e., a, u, and m are subject to death; that is, are not beyond the pale of death; but when used in meditating on the atman in combination, the syllable ‘Om,’ with the three matras, being used at the time of contemplation by the worshipper, in respect of every one of the three aspects of Brahman. Contemplated, i.e., the Vaisvanara or Visva representing the waking condition, the Hiranyagarbha or Taijasa representing the dreaming condition and the Isvara or Pragna representing the sleeping condition, the person meditating who knows this division of the matras of ‘Om’ does not shake. One who knows this, cannot possibly be shaken; because, the Purushas representing the waking, dreaming and sleeping states, with their respective places, are seen as one, with the letter ‘Om’ of three matras; such a knower having become the Âtman of all and one with ‘Om’ from whence could he move and where?