al-Waaqidi said: "When Huracal [Hercules] learned that Umar bin al-Khattab, raadi Allahu anhhu, had assumed the khilaafah after Abu Bakr as-Siddiq, raadi Allahu anhu, he gathered the notables of his nation. A speaker stood before them in the church, and said, 'O people! Be cautious, and again, be cautious before the matter comes to pass and harm befalls us and the palaces are destroyed... Truly, I know that the Religion of these people will be victorious over every religion.'
Then he called for who was known as Talee'ah bin Maaraan, and he guaranteed for him money, and he said to him, 'Proceed from here to Yathrib and see how to best kill Umar bin al-Khattaab.'
So Talee'ah prepared himself and traveled until he reached the city of Rasul Allah, sall Allahu alayhi wa sallam, and he lurked inside of it, until he found Umar supervising the wealth of the orphans and inspecting their gardens. So he climbed up on a tree whose branches were entwined, and hid behind its leaves. Umar, raadi Allahu anhu, approached the tree that he was hiding in, and lay under it and used a rock as his pillow. So when Umar slept, he made up his mind to go down and kill him, but a beast approached from the wild and he encircled Umar and began to lick his feet, and a voice called,
'O Umar, you were just, so you were safe!'
So when Umar arose, the beast left and the man came down and threw himself at Umar and kissed his hands and said, 'You are dearer to me than my mother and father!' Then he informed him of what he was going to do and he became Muslim at Umar's hands."
**
And in another narration, from al-Waaqidi himself, he said: "When Huracal spoke, Jiblah bin al-Ayham arose and said, 'O glory of the Romans! We may kill these Arabs by killing their khalifah, Umar, in al-Madinah. If you sent to him a man from the people of Ghassaan to kill him, then it will cause their failure and allow us to seize ash-Shaam from their hands.'
So Huracal said, 'This is something we should not have hope in, but the nafs is pleased to hear it. Do what you want.'
So Jiblah sent from his people a man who was known as Waathiq bin Musaafir al-Ghassaani, and he was courageous and fearless in wars. It was said to him, 'Go forth to Yathrib, hopefully you will kill Umar.' And he promised him for Umar's death whatever he wanted and asked for of money.
So Waathiq bin Musaafir went forth until he entered al-Madinah one night, so when it was the morning, Umar bin al Khattab prayed with the people the morning prayer, and he supplicated, and then went out to the outskirts of al-Madinah to gather the news of the mujaahideen in ash-Shaam. So he preceded him and waited for him atop a tree in the garden of ad-Dahdaah al-Ansaari, and he covered himself with its branches. Then Umar left the outskirts of al-Madinah when the heat became excessive, and returned alone and approached the garden and entered it, and lay in its shade. So when he slept, Waathiq made up his mind to kill him, and to get down from the tree and unsheath his dagger, but found himself faced with a lion who approached Umar and encircled him and sat at his feet, licking them. He stood until Umar arose, and then he climbed down the tree and kissed Umar's hands and said
, 'O Umar! Surely you have been just and so you are safe wallahi, by the living creatures that preserve you and the beasts that protect you and the angels that are sincere to you and the jinn that know you!' Then he told him of his matter and became Muslim at his hands."
**
And biographers have narrated that there came to Umar, raadi Allahu anhu, al-Harmazaan, the king of al-Ahwaaz, as a prisoner in the 17th year of the hijrah. And with him was a delegation, among them was Anas bin Maalik and al-Ahnaf bin Qays. So when they reached with him to al-Madinah, they clothed him in his garments made of silk, and they placed on his head his crown, which was crowned with rubies, so that Umar and the Muslims would see him in his usual appearance while in his kingdom. They looked for Umar and could not find him, so they asked about him and were told he was in the masjid.
They went to the masjid and found him sleeping. So they sat close to him and al-Harmazaan said, "Where is Umar?"
They said, "That is him."
He said, "Where are his guards and his stewards?"
They said, "He has no guard nor any steward."
So al-Harmazaan looked at Umar and said,
"You were just [to the people], so you were safe [from them], so you slept [without fear]."
Umar arose due to the noise and said, "Al-Harmazaan?"
They said, "Yes, Ameer al-Mu'mineen."
He said, "
Praise be to Allah who humiliated with Islam him and his likes."
[From the book,
Manaaqib Umar bin al-Khattaab, pgs 14-15]
http://talk.islamicnetwork.com/showthread.php?t=12934