Galatians 5:9
A little bit of yeast permeates the whole batch of dough [i.e., a few people can influence everyone else to do the wrong thing in this matter].
1 Corinthians 15:33
Do not be fooled; bad company ruins good moral behavior.
Matthew 16:6-12
Jesus said to them, "Pay attention and watch out for the leavening [effect] of the Pharisees and Sadducees."
Matthew 23:33
You snakes! You children of snakes! How do you expect to escape being judged [and condemned] in hell?
Mark 8:15
Then Jesus ordered them, saying, "Pay attention and watch out for the leavening [effect] of the Pharisees and Herod." [Note: By "Herod" is probably meant the Herodians, who were a party favorable to King Herod and, along with the Pharisees and Sadducees, were out to get Jesus. See Matt. 16:6].
Luke 12:1
About this time, while a crowd of many thousands had assembled, [so large that] people were trampling on one another, Jesus first began telling His disciples, "Watch out for the leavening [effect] of the Pharisees, which is hypocrisy.
Luke 13:21
It is similar to yeast, which a woman worked into three batches of dough, until the dough was completely permeated [by it]."
1 Corinthians 5:6-7
Your boasting is not good. Do you not know that a little yeast can leaven the whole batch of dough?
2 Timothy 2:17
and their talk will spread like gangrene. Among these people are Hymenaeus and Philetus,