Manava Dharmashastra 4.106

4.106

prāduṣkṛteṣv agniṣu tu vidyutstanitaniḥsvane
sajyotiḥ syād anadhyāyaḥ śeṣe rātrau yathā divā //

But when lightning and the roar of thunder (are observed) after the sacred fires have been made to blaze, the stoppage shall last as long as the light (of the sun or of the stars is visible); if the remaining (above-named phenomenon, rain, occurs, the reading shall cease), both in the day-time and at night.