Jaiminīya Upaniṣad Brāhmaṇa 2.15.3

2.15.3

atho ha prokte 'śane brūyāt samintsvāgnim iti
sa yathā prokte 'śane śreyāṁsam pariveṣṭavai brūyāt tādṛk tat /

And when the meal has been announced, he should say: 'Kindle Agni!' That is just as when a meal has been announced, one would tell an elder to serve [food].