While Atri Muni was engaged in these severe austerities, a blazing fire came out of his head by virtue of his breathing exercise, and that fire was seen by the three principal deities of the three worlds.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
तप्यमानं त्रिभुवनं प्राणायामैधसाग्निना । निर्गतेन मुनेर्मूर्ध्नः समीक्ष्य प्रभवस्त्रयः
tapyamānaṃ tribhuvanaṃ prāṇāyāmaidhasāgninā | nirgatena munermūrdhnaḥ samīkṣya prabhavastrayaḥ
SB 4.1.21