Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.3.33

3.9.3.33

yadyukthyaḥ syāt | madhyamam paridhimupaspṛśettrayaḥ paridhayastrīṇyukthānyetairu hi tarhi yajñaḥ pratitiṣṭhati yadyu atirātro vā ṣoḍaśī vā syānnaiva juhuyānna madhyamam paridhim upaspṛśetsamudyaiva tūṣṇīmetya prapadyeta tadyathāyathaṃ yajñakratūnvyāvartayati

And if it be an Ukthya, let him touch the middle enclosing-stick,--there are three enclosing-sticks and three recitations (uktha); and by means of them the sacrifice is there established. And if it be either an Atirâtra or a Shodasin, let him neither make an oblation nor touch the middle enclosing-stick; having merely muttered (the above verse), let him silently betake himself (to the Havirdhâna) and enter it. In this way he duly distinguishes the forms of sacrifice from one another.