Bhagavad Gita Chapter 8, Verse 25

धूमो रात्रिस्तथा कृष्ण: षण्मासा दक्षिणायनम् | तत्र चान्द्रमसं ज्योतिर्योगी प्राप्य निवर्तते ||

dhūmo rātris tathā kṛṣṇaḥ ṣaṇ-māsā dakṣiṇāyanam tatra cāndramasaṁ jyotir yogī prāpya nivartate

Smoke, night, the dark fortnight, the six months of the southern solstice—departing by this path, the yogi attains the lunar light and returns.

Krishna describes the path of darkness: 'Dhumo ratris tatha krishnah shanmasa dakshinayanam'—smoke (dhumah), night (ratrih), the dark fortnight (krishnah), the six months (shanmasa) of the southern solstice (dakshinayanam). 'Tatra chandramasam jyotir yogi prapya nivartate'—departing (tatra) by that path, the yogi (yogi) having attained (prapya) the lunar light (chandramasam jyotih), returns (nivartate). This is the path of darkness—the obscure path that leads to rebirth. Those who depart during these inauspicious times (smoke, night, dark fortnight, southern solstice) attain the lunar light and return to the material world. This is the path of rebirth—return to the cycle of birth and death. Understanding this helps you avoid: don't cultivate the state of consciousness that leads to this path. Instead, cultivate the path of light that leads to liberation.