Shiva Purana
अथावसरमासाद्य रुद्रः सर्वान्तकः प्रभुः ॥ स्वांशेन तनयो जज्ञे द्रोणस्य स महाबलः॥। १३ ॥
Taking the due opportunity, lord Śiva, the annihilator of all and very powerful was born as Droṇa’s son through a part of himself.
english translation
athAvasaramAsAdya rudraH sarvAntakaH prabhuH ॥ svAMzena tanayo jajJe droNasya sa mahAbalaH॥। 13 ॥
hk transliteration by Sanscript