Pitṛgaṇa-Vibhāga (Classification of the Pitṛs) and the Śrāddha–Soma Nourishment Cycle
श्लेषं संसक्तयोर्ज्ञात्वा शङ्कितः किल वृत्रहा / ताभ्यां मैथुनशक्ताभ्यामपत्योद्भवभीरुणा
śleṣaṃ saṃsaktayorjñātvā śaṅkitaḥ kila vṛtrahā / tābhyāṃ maithunaśaktābhyāmapatyodbhavabhīruṇā
Knowing their close embrace, Vṛtrahā (Indra) grew anxious indeed; for both were endowed with the power of union, and he feared the birth of offspring.