MuU 3.1.5
सत्येन लभ्यस्तपसा ह्येष आत्मा सम्यग्ज्ञानेन ब्रह्मचर्येण नित्यम् । अन्तःशरीरे ज्योतिर्मयो हि शुभ्रो यं पश्यन्ति यतयः क्षीणदोषाः
satyena labhyastapasā hyeṣa ātmā samyagjñānena brahmacaryeṇa nityam | antaḥśarīre jyotirmayo hi śubhro yaṃ paśyanti yatayaḥ kṣīṇadoṣāḥ
Sanskrit for this text is pending; the English follows the translator's numbering.
By truthfulness, indeed, by penance, right knowledge, and abstinence must that Self be gained; the Self whom spotless anchorites gain is pure, and like a light within the body.
Translated by F. Max Müller