Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.3.5

2.3.3.5

sa yatra mriyate | yatrainamagnāvabhyādadhati tadeṣo 'gneradhijāyate sa eṣa putraḥ sanpitā bhavati

And when he dies, and they place him on the (funeral) fire, then he is reproduced from out of the fire; and he (Agni) who heretofore was his son, now becomes his father.