Shatapatha Brahmana 6.7.1.23

6.7.1.23

sā yadukhā nāma | etadvai devā etena karmaṇaitayāvṛtemāṃlokānudakhananyadudakhanaṃstasmādutkhītkhā ha vai tāmukhetyācakhate paro 'kṣam paro 'kṣakāmā hi devāḥ

And as to why it is called 'Ukhâ;'--by means of this sacred performance and this process the gods at that time dug out these worlds; and inasmuch as they so dug out (ut-khan), it (the pan representing the worlds) is called 'utkhâ,'--'utkhâ' being what they mysteriously (esoterically) call 'ukhâ,' for the gods love the mysterious.