Śatapatha Brāhmaṇa ("of a hundred paths") 2.2.2.16

2.2.2.16

tamuddīpya saminddhe | iha yakṣya iha sukṛtaṃ kariṣyāmītyevainametatsaminddhe yo 'syaiṣo 'ntarātmannāgnirāhito bhavati

Having kindled it, he makes it blaze, thinking, 'Herein I will worship, herein I will perform the sacred work!' Thereby he makes blaze that fire which has been established in his innermost soul.