Śatapatha Brāhmaṇa ("of a hundred paths") 6.3.1.2

6.3.1.2

te yadabruvan cetayadhvamiti citimicateti vāva tadabruvanyaccetayamānā apaśyaṃstasmāccitirāhutirvai yajño yadiṣṭvāpaśyattasmādiṣṭakā

Now when they said, 'Meditate ye!' they doubtless meant to say, 'Seek ye a layer!' and inasmuch as they saw it whilst meditating (ketay), therefore it is a layer (kiti). And the libation is a sacrifice; and inasmuch as he saw it after sacrificing (ishtvâ), it is a brick (ishtakâ).