Śatapatha Brāhmaṇa ("of a hundred paths") 2.1.3.7

2.1.3.7

atha yaḥ kāmayeta | kṣatraṃ śriyā yaśasā syāmiti grīṣme sa ādadhīta kṣatraṃ vai grīṣmaḥ kṣatraṃ haiva śriyā yaśasā bhavati

And whosoever desires to become a power (kshatra) in prosperity and renown, let him set up his fires in summer,--for the summer is the nobility (kshatra),--and he will certainly become a power in prosperity and renown.