Bhagavad Gita 10.20 Chapter 10, Verse 20

अहमात्मा गुडाकेश सर्वभूताशयस्थितः ।
अहमादिश्च मध्यं च भूतानामन्त एव च ॥१०.२०॥

ahamātmā guḍākeśa sarvabhūtāśayasthitaḥ
ahamādiśca madhyaṃ ca bhūtānāmanta eva ca

Meaning

O Gudakesha, I am the Self seated in the hearts of all beings. I am the beginning, the middle and the end of all beings.

Newly written by Bhajan Dhun — scholarly review in progress.

Reference: Bhagavad Gita 10.20 (Chapter 10, The Yoga of Divine Glories (Vibhuti Yoga), Verse 20)