Brahmārpaṇaṃ brahma havir. In many Indian homes and schools it is said before the first mouthful.
It is Bhagavad Gītā 4.24. Kṛṣṇa is describing a sacrifice in which everything is Brahman: the act of offering, the offering itself, the fire it is poured into, the one who offers. Seen that way, the work and its reward are one.
Said at the table, it turns a meal into that sacrifice. The food, the hunger and the one who eats are all the same offering.
Every meal, an offering.
Going deeper
In chapter 4 Kṛṣṇa is explaining how action can stop binding a person. 4.23 says that someone whose attachments are gone, whose mind rests in knowledge, and who acts only as an offering, has their karma dissolved. Then comes the verse families say at the table. 4.24 looks at the sacrifice from the inside: the instrument of offering is Brahman, the offering is Brahman, the fire is Brahman, and the offering is made by Brahman. Whoever sees the act this way reaches Brahman by that very act. The verse that follows, 4.25, lists other ways that yogis offer sacrifice, so this is one of several, not the only one. Said before a meal, it asks you to see the food, the hunger and the person eating as one offering. You can read the whole teaching in chapter 4, and what the Gītā says about karma follows the same idea through other verses.