Nip the evil in the Bud

or

The Arab and His Camel

An Arab had a camel. One cold night the Arab lay asleep inside the tent while the camel stood outside.

At midnight the camel awoke his master and requested him to allow him to put his head inside the tent as it was bitter cold outside. The Arab allowed him to do so.

After a while, the camel asked the Arab if he might put his neck inside the tent. The Arab did not object to do it.

Soon after the camel requested him again to allow him to bring his legs inside. The Arab agreed. Now the camel stood completely inside the twit. But as there was not space enough for both of them he pushed the Arab outside to shiver in cold.

Moral:

Nip the evil in the bud.