Agniveshyagrihyasutra 3.8.3.19

3.8.3.19

vijñāyate agniṃ citvā sautrāmaṇyā yajeta maitrāvaruṇyāmikṣayā vā iti kāṭhakāgnīnāṃ brāhmaṇam \

It is known [from scripture]: 'Having piled the fire, one should sacrifice with the Sautrāmaṇī or with an āmikṣā offering to Mitra and Varuṇa'—such is the Brāhmaṇa passage of the Kāṭhaka fires.