Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.3.11

3.9.3.11

tadāhuḥ | kaḥ prātaranuvākasya pratigara iti jāgraddhaivādhvaryurupāsīta sa yannimiṣati sa haivāsya pratigarastadu tathā na kuryādyadi nidrāyādapi kāmaṃ svapyātsa yatra hotā prātaranuvākam paridadhāti tatpracaraṇīti srugbhavati tasyāṃ caturgṛhītamājyaṃ gṛhītvā juhoti

Here now they say, 'What is the (Adhvaryu's) response to the morning-prayer?' The Adhvaryu should wait through (the prayer) waking, and when he blinks, this is his response. But let him not do this; if he fall asleep (again) he may as well sleep. When the Hotri brings his morning-prayer to a close,--there is an offering-spoon called Prakaranî,--having therein taken ghee in four ladlings, he (the Adhvaryu) offers it.