Jñāneśvarī (commentary on the Bhagavadgītā) 2.78

2.78

tetha sudarśanācī dyuti |
teci vidyullatā jhaḷakatī |
gaṃbhīra vācā te āyatī |
garjanecī ||

There, the radiance of the Sudarśana discus / flashes forth as the streaks of lightning, / and his deep speech / has the bearing of thunder.