Valmiki Ramayana Bala Kanda Sarga 65 Shloka 8

अनुच्छ्वसमानस्य while he was suspending his breath, तस्य Visvamitra's, मूर्ध्नि on his head, धूम: smoke, व्यजायत emanated, येन by which, त्रैलोक्यम् three worlds, सम्भ्रान्तम् agitated, आदीपितमिव अभवत् was as thoughset on fire.

While his breath, was suspended, smoke emanated from his head which frightened the three worlds. It appeared as though they were on fire.