Chapter 5 · The Yoga of Renunciation · Krishna said
Bhagavad Gita 5.24 — The light within
योऽन्तःसुखोऽन्तरारामस्तथान्तर्ज्योतिरेव यः। स योगी ब्रह्मनिर्वाणं ब्रह्मभूतोऽधिगच्छति ॥
yo'ntaḥsukho'ntarārāmastathāntarjyotireva yaḥ | sa yogī brahmanirvāṇaṃ brahmabhūto'dhigacchati ||
Meaning
One whose happiness, delight and light are all within — that yogi becomes one with Brahman and attains the peace of Brahman (brahma-nirvana).