Bhagavad Gita: Chapter 2, Verse 69

या निशा सर्वभूतानां तस्यां जागर्ति संयमी ।
यस्यां जाग्रति भूतानि सा निशा पश्यतो मुनेः ॥ २-६९ ॥

yā niśā sarva-bhūtānāṁ tasyāṁ jāgarti saṁyamī
yasyāṁ jāgrati bhūtāni sā niśā paśyato muneḥ 2.69

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