MUṆḌAKA UPANISHAD · 3.1.5

सत्येन लभ्यस्तपसा ह्येष आत्मा
सम्यग्ज्ञानेन ब्रह्मचर्येण नित्यम् ।
अन्तःशरीरे ज्योतिर्मयो हि शुभ्रो
यं पश्यन्ति यतयः क्षीणदोषाः ॥ ५॥

satyena labhyastapasā hyeṣa ātmā
samyagjñānena brahmacaryeṇa nityam ।
antaḥśarīre jyotirmayo hi śubhro
yaṃ paśyanti yatayaḥ kṣīṇadoṣāḥ ॥ 5॥

The Self can always be won by truth, by self-discipline, by integral knowledge, by a life of purity, — this Self that is in the inner body, radiant, made all of light whom by the perishing of their blemishes the doers of askesis behold.

Sri Aurobindo · CWSA 18, p. 143