Bhagavad Gita · 2.69

या निशा सर्वभूतानां तस्यां जागर्ति संयमी।यस्यां जाग्रति भूतानि सा निशा पश्यतो मुनेः॥

yā niśhā sarva-bhūtānāṁ tasyāṁ jāgarti saṁyamī yasyāṁ jāgrati bhūtāni sā niśhā paśhyato muneḥ

What is night for all beings is the time of awakening for the self-controlled; and what is the time of awakening for all beings is night for the sage who sees.

— Bhagavad Gita 2.69

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)