Śrīmad-Bhāgavatam · Text 6.9.52
Who is speaking and story frame
स वा अधिगतो दध्यङ्ङश्विभ्यां ब्रह्म निष्कलम् ।
यद्वा अश्वशिरो नाम तयोरमरतां व्यधात् ॥ ५२ ॥
sa vā adhigato dadhyaṅṅ
aśvibhyāṁ brahma niṣkalam
yad vā aśvaśiro nāma
tayor amaratāṁ vyadhāt
That saintly Dadhyañca, who is also known as Dadhīci, personally assimilated the spiritual science and then delivered it to the Aśvinī-kumāras. It is said that Dadhyañca gave them mantras through the head of a horse. Therefore the mantras are called Aśvaśira. After obtaining the mantras of spiritual science from Dadhīci, the Aśvinī-kumāras became jīvan-mukta, liberated even in this life.
Read Śrīla Prabhupāda's purport on Vedabase.io