At the end of Brahmā’s one hundred years, when his meditation was complete, he developed the required knowledge, and as a result he could see in his heart the Supreme within himself, whom he could not see before with the greatest endeavor.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
कालेन सोऽजः पुरुषायुषाभि- प्रवृत्तयोगेन विरूढबोधः । स्वयं तदन्तर्हृदयेऽवभात- मपश्यतापश्यत यन्न पूर्वम्
kālena so'jaḥ puruṣāyuṣābhi- pravṛttayogena virūḍhabodhaḥ | svayaṃ tadantarhṛdaye'vabhāta- mapaśyatāpaśyata yanna pūrvam
SB 3.8.22