From: Anecdotes of the Pious Ones, # 74, v.1
Abdul Malik bin Marwan died in 86 Hijri, after 21 years of tyranny. His son Waleed succeeded him. He decided to bring about some justice to please the populus. He tried hard to please the people of Madinah, in particular, as it was one of the two sacred Muslim cities where some decendants of the Prophet's companions, and some famous narrators lived.
That is why he fired Hisham bin Ismail Makhzooni, the father-in-law of Abdul Malik, who was the cruel and unjust governor of Madinah.
Hisham bin Ismail had reached the extreme cruelty and offense to the people of Madinah. Saeed bin Museeb, who was a respectable and famous narrator was beaten sixty lashes, was made to wear a coarse robe, while sitting on a camel and being walked through the streets of Madinah, because he had refused to give allegience. He had commited numerous offenses towards the family of the Prophet (pbuh&hf), specially Imam Zainul 'Abideen (as).
Walid fired Hisham and instead hired Umar bin 'Abdul 'Aziz, his young cousin who was popular for his sincerity and his justice.
Umar ordered that Hisham bin Ismail be brought in front of Marwan's house and whoever has any complaint against him, get his right. People would come, in groups, and offered him curses, and harsh words.
Hisham was afraid of Imam Zainul 'Abideen's (as) revenge. He thought to himeself that Imam will bring him nothing less than death due to the cruelty done to his family.
But the Imam (as) had told his followers: "Our character isn't one of kicking the fallen ones. Neither do we avenge the enemy when he has fallen and weak. Our character is that of assisting the poor and the needy."
As the Imam and his followers approached him, Hisham turned pale and expected a cold blooded murder at any moment.
But just apposite to his expectation, Imam (as), in his usual manner of a Muslim must aid a Muslim, called on him: "Salaamun 'Alaikum."
After greeting him, the Imam (as) offered: "If there is anything I could do for you, I am ready to do."
The people of Madinah, also, stopped punishing Hisham after that moment. 
 Bihar v. 11, p. 17 & 27. And "Al Imam Sadiq Sayyed al Ahl" translated by Husayn Wijdani, p. 92.