Once upon a time a heathen came to Shammai and said to him, "I should like to become a Jew if you will teach me the whole of the Law whilst I am standing on one leg."

When he heard this, Shammai took a measuring rod used by builders and drove him away with it.

The heathen left Shammai and went to Hillel, and asked him whether he would accept him as a proselyte, and whether he would teach him the whole Torah while he was standing on one leg.

Hillel accepted him and said, "Yes, I will teach you the whole, Torah while you are standing on one leg." Then, he said to the heathen, "Keep this commandment, 'Do not unto thy neighbor what thou wouldst not like to have done to thyself.' This is the fundamental principle of the law. All the rest is a commentary upon it. Now go and study it."

Thus Hillel taught him the whole Torah while he was standing on one leg.