Śatapatha Brāhmaṇa ("of a hundred paths") 6.2.2.39

6.2.2.39

tadāhuḥ | naitena paśuneṣṭvopari śayīta na māṃsamaśnīyānna mithunamupeyātpūrvadīkṣā vā eṣa paśuranavakLptaṃ vai tadyaddīkṣita upari śayīta yanmāṃsamaśnīyādyanmithunamepeyāditi netvevaiṣā dīkṣā neva hi mekhalāsti na kṛṣṇājinamiṣṭakāṃ vā etāṃ kurute tasmādu kāmamevopari śayītaitadu sarvamannaṃ yadate paśavastadasyātrāptamārabdham bhavati tadyāni kāni cāmadhuno 'śanāni teṣāmasya sarveṣāṃ kāmāśanaṃ yadi labheta mithunaṃ tu nopeyātpurā maitrāvaruṇya payasyāyai tasyopari bandhuḥ

Here now they say, 'After he has performed that animal offering, he must not sleep upon (a couch), nor eat flesh, nor hold carnal intercourse; for that animal sacrifice is the first Dîkshâ, and improper surely it would be, were the initiated to sleep upon (a couch), or were he to eat flesh, or hold carnal intercourse.' But in no way is this a Dîkshâ, for there is neither a girdle, nor a black antelope skin; but he makes this the first brick: let him therefore, if he like, sleep upon (a couch); and whatever food animals here eat, all that is here obtained and taken possession of by him; and whatever kinds of food there are other than honey, of all those he may eat at pleasure, if he can get them. Carnal intercourse, however, he may not hold prior to the (offering of) clotted curds to Mitra and Varuna: the purport of this (will be explained) hereafter.