The Prophet once had to borrow some money from a Jew by the name of Zayd ibn Sana. Zayd ibn Sana says that a couple of days before the fixed date for the payment of debt, he found the Prophet sitting with a number of his companions next to a wall. He went up to the Prophet, caught hold of his clothes, and said to him harshly, “Mohammad, why don’t you pay me my due? From what I know of your family, they all put off paying their debts.”
Umar ibn al-Khattab, a companion of the Prophet, became very angry on hearing this. “Enemy of God,” he said, “is that the way you address the Prophet of God? If it wasn’t for the prophet, I swear by God that I would have cut off your head with my sword.” But the Prophet kept on looking calmly at Zayd ibn Sana. Then he addressed Umar. “Umar,” he said, “Zayd and I deserved better treatment from you. You should have told me to be better at paying my debts, and him to be better at demanding them. Take him with you, Umar, and pay him his due; in fact, give him 20 sa’as (one sa’a is equivalent to 2.5 kg of wheat) of dates extra, because you have alarmed him with your threats.”
After this behaviour on the part of the Prophet, Zayd ibn Sana became a follower of the Prophet. He explained why after the above incident he came to believe that the Prophet was indeed a prophet. He says that when he saw the Prophet, he found on his face all the signs of prophethood but one, and that was the unshakable forbearance which a prophet should evince. An excess of ignorance on another’s part should only result in an excess of forbearance on his part. These were the traits which he had wanted to test in the Prophet, This was why he deliberately behaved harshly with the Prophet–to see how he would respond when provoked.