Shatapatha Brahmana 5.5.5.11

5.5.5.11

sarvānvā eṣa yajñakratūnavarunddhe | sarvā iṣṭīrapi darvihomānyo rājasūyena yajate devasṛṣṭo vā eṣeṣṭiryattraidhātavyanayā me 'pīṣṭamasadanayāpi sūyā iti tasmādvā eṣā rājasūyayājina udavasānīyeṣṭhirbhavati

And, verily, he who performs the Râgasûya gains for himself all sacrificial rites, all offerings, even the spoonful-oblations; and this offering, the Traidhâtavî (ishti), is instituted by the gods: 'May this offering also be performed by me, may I be consecrated by this one also!' thus he thinks, and therefore this is the completing offering for him who performs the Râgasûya.