Srimad-Bhagavatam: Canto 6 - Chapter 1 - Verse 40
Sanskrit:
विवस्वत: श्राद्धदेवं संज्ञासूयत वै मनुम् ।मिथुनं च महाभागा यमं देवं यमीं तथा ।सैव भूत्वाथ वडवा नासत्यौ सुषुवे भुवि ॥ ४० ॥
ITRANS:
vivasvataḥ śrāddhadevaṁsaṁjñāsūyata vai manummithunaṁ ca mahā-bhāgāyamaṁ devaṁ yamīṁ tathāsaiva bhūtvātha vaḍavānāsatyau suṣuve bhuvi
Translation:
Saṁjñā, the wife of Vivasvān, the sun-god, gave birth to the Manu named Śrāddhadeva, and the same fortunate wife also gave birth to the twins Yamarāja and the river Yamunā. Then Yamī, while wandering on the earth in the form of a mare, gave birth to the Aśvinī-kumāras.