Bhagavatapurana 2.5.42

2.5.42

bhūrlokaḥ kalpitaḥ padbhyāṃ bhuvarloko 'sya nābhitaḥ /
svarlokaḥ kalpito mūrdhnā iti vā lokakalpanā //

42. Or, this arrangement of worlds may be conceived thus (is partly otherwise described thus): Bhurloka issued from His feet, Bhuvar-loka from His navel, and Svarloka from His head.