Chandogya Upanishad 8.1.3

8.1.3

yāvān vā ayam ākāśas tāvān eṣo 'ntarhṛdaya ākāśaḥ \
ubhe asmin dyāvāpṛthivī antar eva samāhite \
ubhāv agniś ca vāyuś ca sūryācandramasāv ubhau vidyun nakṣatrāṇi \
yac cāsyehāsti yac ca nāsti sarvaṃ tad asmin samāhitam iti \\801.3\

If the disciples should say to him, 'In this city of Brahman in that which is a small mansion in the shape of a lotus and in the small inner Ākāśa within—what is it that lies there which should be sought, which one should desire to understand?—he should say in reply, 'As large indeed as is this Ākāśa, so large is that Ākāśa in the heart. Within it, indeed, are contained both heaven and earth, both fire and air, both the sun and the moon, lightning and the stars. Whatever there is of him in this world and whatever is not, all that is contained within it.'