Śatapatha Brāhmaṇa ("of a hundred paths") 11.1.1.2

11.1.1.2

sa yo'māvāsyāyāmagnī ādhatte yathā vivṛtāyāṃ dvāri dvārā puram prapadyeta sa tata eva svargaṃ lokamiyādevaṃ tadyo'māvāsyāyāmādhatte

And when one lays down the two fires at new moon,--even as one would enter a stronghold by the gate, when the gate is open, and would thence reach the world of heaven, so it is when one lays down the fires at new moon.