Abdullah ibn Ali was the uncle of Saffah, the founder of the Abbasid rule. He was a very harsh, cruel, and bloodthirsty ruler.
He uprooted the Banu Umayya from Sham and established the foundation of the Abbasid rule there.
After entering Sham, he sent a message to the famous scholar of that place, Imam Awza'i (may Allah have mercy on him), to appear in his court.

Imam Awza'i (may Allah have mercy on him) understood Abdullah ibn Ali's intention. So, instead of responding to his request, he remained in hiding for three days. But in the end, it was no longer possible to avoid it. He went and appeared in Abdullah ibn Ali's court.

Imam Awza'i (may Allah have mercy on him) later described that terrifying meeting, saying:

I entered before him. I saw him sitting on a cot. In his hand was a bamboo cane. To his right and left stood soldiers dressed in black. In their hands were unsheathed swords, and at their waists were iron scabbards.

I greeted him.

He did not return my greeting. Instead, he began tapping the ground with the bamboo cane in his hand. Then, looking at me, he said:

"O Awza'i! What we have done, that is, freeing the people and the country from the hands of the Umayyad tyrants—do you consider this to be counted as Jihad and the work of guarding the borders?"

Imam Awza'i (may Allah have mercy on him) replied:
"The Messenger of Allah (peace and blessings of Allah be upon him) said, 'Actions are based on intentions. Every person will get the result according to his intention.'"

As soon as I finished speaking, he began tapping the bamboo cane even harder than before. The soldiers standing around him also tightened their grip on the hilts of their swords one by one.

Then he looked at me and said:

"O Awza'i! What do you say about the blood of the people of Banu Umayya?"

I said:

"The Messenger of Allah (peace and blessings of Allah be upon him) said:

'It is not lawful to shed the blood of a Muslim except for three reasons: If someone kills a Muslim unjustly, if a married person commits adultery, and if someone leaves the religion of Islam and separates from the Muslim community.'"

Hearing my answer, Abdullah ibn Ali began tapping the bamboo cane even harder. Then he said:

"Then what do you say about their wealth?"

I said:

"If the wealth in their hands was acquired unlawfully, then it is unlawful for you as well. And if it was acquired lawfully, then it will not be lawful for you without a Sharia-compliant method."

This time he began tapping with the cane even more violently than before.

After a while, he suddenly said:

"Then shall I appoint you to the position of judge?"

I said:

"Your predecessors never troubled me with this matter. And I wish that the tradition of favor they started toward me continues."

He looked at me and said:

"It seems you want to leave here?"

I said:

"I have some female relatives at home. They are helpless and need care and protection. Because of me, their hearts are now heavy with anxiety."

After saying these words, I began to wait in my heart—thinking that now my head would roll onto the ground in front of me!

But after a while, he said to me:

"You go."

I then came out from there.

After going some distance, I suddenly saw one of the Amir's messengers running toward me from behind. In his hand were two hundred dinars. He came and said, "The Amir has told you to spend these for your own needs."

I was a little afraid that if I did not accept this money now, Abdullah ibn Ali might harm me. So, out of helplessness, I accepted it and immediately gave all two hundred dinars in charity.

The three days I was in hiding, I had fasted all three days. When the Amir learned of this, he invited me to break my fast with him one day. I flatly refused to break my fast with a tyrant.
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Because of such a personality, Imam Awza'i (may Allah have mercy on him) had a lot of influence in Sham. His influence and authority there were so strong that for the common people, his instructions carried more weight than the ruler's instructions.

Once, a governor of Sham thought about taking strict action against him. Then his companions said to him, "Leave him alone. By Allah! If he orders the people to kill you, the people of Sham will do so without hesitation."

After Imam Awza'i passed away, that governor once sat by his grave and said, "May Allah have mercy on you. By Allah! I used to fear you more than the Caliph who sent me here as governor!"
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Source: Al-Bidaya wan-Nihaya, 10/118, see the discussion of 157 AH.