From The Washington Post-
A story about Billy Graham goes something like this: In 1949 or 1950, after one of his famous evangelistic meetings, Graham returned to his hotel room to find a naked woman lying on his bed, ready to seduce him in an attempt to destroy his ministry. Graham, cautious and humble as usual, fled the hotel room and immediately implemented a rule that would come to bear his name: From that day forward, Graham would not travel (including by car), eat or meet alone with a woman other than his wife, Ruth.
The Billy Graham Rule was soon adopted by evangelical pastors and business executives. Men in positions of influence wanted to “flee from sexual immorality” and be “above reproach” (both biblical commands), as well as abstain from “every appearance of evil.” Aware of how many Christian leaders have been felled by sexual immorality, many of these men were taking sincere steps to guard their marriages from infidelity and their hearts from lust.