Bhagavad Gita 7.10

Know, O Arjuna, that I am the eternal seed of being; I am the intelligence of the intelligent, the splendour of the resplendent.

बीजं मां सर्वभूतानां विद्धि पार्थ सनातनम्।
बुद्धिर्बुद्धिमतामस्मि तेजस्तेजस्विनामहम्॥

bījaṃ māṃ sarvabhūtānāṃ viddhi pārtha sanātanam|
buddhirbuddhimatāmasmi tejastejasvināmaham||

English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).