“In the passage about the bush”
But concerning the dead rising, have you not read about the burning bush in the Book of Moses, how God told him, 'I am the God of Abraham, the God of Isaac, and the God of Jacob'? (Mark 12:18–27 BSB)
What it sounds like today
The seven-brothers puzzle looks bizarre, and Jesus' answer seems to dodge it.
The cultural key
The Sadducees' riddle is built on levirate marriage (Deuteronomy 25:5–6): a man must marry his brother's childless widow to raise an heir. The Sadducees, the temple aristocracy, accepted only the books of Moses as fully authoritative and denied resurrection, so their puzzle is a reductio: whose wife in the resurrection? Jesus answers from their own turf, the Torah itself: at the bush (Exodus 3:6), God says 'I am', present tense, 'the God of Abraham,' centuries after Abraham died. Mark preserves how texts were cited in a world without chapter and verse numbers: 'in the passage about the bush' names the section by its landmark. Jesus also closes with a verdict Matthew lacks: 'You are quite wrong.'
Recovered meaning
God does not introduce himself by dead men's names. If he still calls himself Abraham's God, Abraham is not gone; covenant relationship outlives the grave. A resurrection proof drawn from the only scriptures his opponents fully conceded.