Bhagavatapurana 3.28.24.p2

3.28.24.p2

nābhi-hradaṃ bhuvana-kośa-guhodara-sthaṃ $ yatrātma-yoni-dhiṣaṇākhila-loka-padmam &

25. He should meditate on his navel deep like a pool on the stomach which is the abode of the whole system of the worlds and in which (navel) grows the lotus which is the home of Brahma and which comprises all the worlds; and also he should contemplate His two nipples which are like two emeralds and look white on account of the rays of His brilliant wreaths of pearls.