Śatapatha Brāhmaṇa ("of a hundred paths") 1.5.3.10

1.5.3.10

atha tanūnapātaṃ yajati | grīṣmo vai tanūnapādgrīṣmo hyāsām prajānāṃ tanūstapati grīṣmameva taddevā avṛñjata grīṣmātsapatnānantarāyaṅgrīṣmamevaiṣa etadvṛṅkte grīṣmātsapatnānantareti tasmāttanūnapātaṃ yajati

After that he pronounces the offering-prayer to Tanûnapât. Tanûnapât, doubtless, is the summer; for the summer burns the bodies (tanûn tapati) of these creatures. The gods, at that time, appropriated the summer, and deprived their rivals of the summer; and now this one also appropriates the summer, and deprives his rivals of the summer: this is the reason why he pronounces the offering-prayer to Tanûnapât.