Mahabharata 13.51.29

स्वाहाकारवषट्कारौ गोषु नित्यं प्रतिष्ठितौगावो यज्ञप्रणेत्र्यो वै तथा यज्ञस्य ता मुखम्

svāhākāravaṣaṭkārau goṣu nityaṃ pratiṣṭhitaugāvo yajñapraṇetryo vai tathā yajñasya tā mukham

Our plain-language meaning of this verse is waiting for scholar review.