CC Ādi 5.102

tāṅra nābhi-padma haite uṭhila eka padma
sei padme haila brahmāra janma-sadma
Word for word: 
tāṅra — His; nābhi-padma — lotus navel; haite — from; uṭhila — grew; eka — one; padma — lotus flower; sei padme — on that lotus; haila — there was; brahmāra — of Lord Brahmā; janma-sadma — the place of birth.
Translation: 
From His navel grew a lotus flower, which became the birthplace of Lord Brahmā.