Matthew 16:12

12 Then they understood that he was not telling them to guard against the yeast used in bread, but against the teaching of the Pharisees and Sadducees.

Read Matthew 16:12 Using Other Translations

Then understood they how that he bade them not beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees.
Then they understood that he did not tell them to beware of the leaven of bread, but of the teaching of the Pharisees and Sadducees.
Then at last they understood that he wasn’t speaking about the yeast in bread, but about the deceptive teaching of the Pharisees and Sadducees.