CC Madhya 24.76
nānyad yat sad-asat-param
paścād ahaṁ yad etac ca
yo ’vaśiṣyeta so ’smy aham
aham — I, the Personality of Godhead; eva — certainly; āsam — existed; eva — only; agre — before the creation; na — never; anyat — anything else; yat — which; sat — the effect; asat — the cause; param — the supreme; paścāt — after; aham — I, the Personality of Godhead; yat — which; etat — this creation; ca — also; yaḥ — who; avaśiṣyeta — remains; saḥ — that; asmi — am; aham — I, the Personality of Godhead.
“ ‘Prior to the cosmic creation, only I exist, and no phenomena exist, either gross, subtle or primordial. After creation, only I exist in everything, and after annihilation only I remain eternally.’
This verse from Śrīmad-Bhāgavatam (2.9.33) was spoken by Lord Kṛṣṇa. For an explanation see Ādi-līlā 1.53.