Śatapatha Brāhmaṇa ("of a hundred paths") 2.4.3.7

2.4.3.7

taṃ vai purāṇānāṃ kuryādityāhuḥ | kṣatraṃ vā indrāgnī netkṣatramabhyārohayāṇīti tau vā ubhāveva navānāṃ syātāṃ yaddhi puroḍāśa itaraścaruritarastenaiva kṣatramanabhyārūḍhaṃ tasmādubhāveva navānāṃ syātām

'Let him prepare it from old (grain),' say some; 'for Indra and Agni are the Kshatra (and he should therefore use old grain for the Vaisvadeva pap) lest he (the sacrificer) should exalt (the Vis) to the level of the Kshatra.' Nevertheless let both (the cake and karu) consist of new (grain); for (by the very fact that) the one is a cake and the other a pap, the nobility is not equalled (by the people): hence they should both consist of new (grain).