Bhagavad Gita 10.20

O Arjuna! I am the Self, seated in the hearts of all beings; I am the beginning, the life, and the end of them all.

अहमात्मा गुडाकेश सर्वभूताशयस्थितः।
अहमादिश्च मध्यं च भूतानामन्त एव च॥

ahamātmā guḍākeśa sarvabhūtāśayasthitaḥ|
ahamādiśca madhyaṃ ca bhūtānāmanta eva ca||

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