A.T. Robertson Commentary Luke 20:16

"He will come and destroy these husbandmen, and will give the vineyard unto others. And when they heard it, they said, God forbid." — Luke 20:16 (ASV)

God forbid (μη γενοιτο). Optative of wish about the future with μη. Literally,

may it not happen . No word "God" in the Greek. This was the pious protest of the defeated members of the Sanhedrin who began to see the turn of the parable against themselves.