Śatapatha Brāhmaṇa ("of a hundred paths") 2.1.2.19

2.1.2.19

te ha devā ūcuḥ | yāni vai tāni kṣatrāṇyabhūvanna vai tāni kṣatrāṇyabhūvanniti tadvai nakṣatrāṇāṃ nakṣatratvaṃ tasmādu sūryanakṣatra eva syādeṣa hyeṣāṃ vīryaṃ kṣatramādatta yadyu nakṣatrakāmaḥ syādetadvā anaparāddhaṃ nakṣatraṃ yatsūryaḥ sa etenaiva puṇyāhena yadeteṣāṃ nakṣatrāṇāṃ kāmayeta tadupertsettasmādu sūryanakṣatra eva syāt

The gods then said, 'They who have been powers, shall no longer (na) be powers (kshatra)!' Hence the powerlessness (na-kshatratvam) of the nakshatras. For this reason also one need only take the sun for one's nakshatra (star), since he took away from them their energy, their power. But if he (the sacrificer) should nevertheless be desirous of having a nakshatra (under which to set up his fires), then assuredly that sun is a faultless nakshatra for him; and through that auspicious day (marked by the rising and setting of the sun) he should endeavour to obtain the benefits of whichever of those asterisms he might desire. Let him therefore take the sun alone for his nakshatra.