Mahabharata 14.72.1

वैशंपायन उवाच · vaiśaṃpāyana uvāca

दीक्षाकाले तु संप्राप्ते ततस्ते सुमहर्त्विजःविधिवद्दीक्षयामासुरश्वमेधाय पार्थिवम्

dīkṣākāle tu saṃprāpte tataste sumahartvijaḥvidhivaddīkṣayāmāsuraśvamedhāya pārthivam

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