Bhagavatapurana 2.10.28

2.10.28

āsisṛpsoḥ puraḥ puryā nābhidvāram apānataḥ /
tatrāpānastato mṛtyuḥ pṛthaktvam ubhayāśrayam //

28. When He thought of going from one body to another and of departing (from the body), the navel was formed as a door-way; and there the organ called apana and the presiding deity Mrityu have been appointed to be; and on these two depends the separation or departing from the body.