Another man who was to be killed was Wahshi ibn Harb who had murdered the uncle of Prophet Mohammad (p). But due to the kindness and mercy of the Prophet, (p) Washshi came to Mohammad (p) to be pardoned for what he had done to his uncle. The Prophet forgave him.
I went out with ‘Ubaidullah bin `Adi Al-Khaiyar. When we reached Hims (i.e. a town in Syria), ‘Ubaidullah bin `Adi said (to me), “Would you like to see Wahshi so that we may ask him about the killing of Hamza?” I replied, “Yes.” Wahshi used to live in Hims. We enquired about him and somebody said to us, “He is that in the shade of his palace, as if he were a full water skin.” So we went up to him, and when we were at a short distance from him, we greeted him and he greeted us in return.
‘Ubaidullah was wearing his turban and Wahshi could not see except his eyes and feet. ‘Ubaidullah said, “O Wahshi! Do you know me?” Wahshi looked at him and then said, “No, by Allah! But I know that `Adi bin Al-Khiyar married a woman called Um Qital, the daughter of Abu Al-Is, and she delivered a boy for him at Mecca, and I looked for a wet nurse for that child.
(Once) I carried that child along with his mother and then I handed him over to her, and your feet resemble that child’s feet.” Then ‘Ubaidullah uncovered his face and said (to Wahshi), “Will you tell us (the story of) the killing of Hamza?”
Wahshi replied “Yes, Hamza killed Tuaima bin `Adi bin Al-Khaiyar at Badr (battle) so my master, Jubair bin Mut`im said to me, ‘If you kill Hamza in revenge for my uncle, then you will be set free.” When the people set out (for the battle of Uhud) in the year of ‘Ainain. ‘Ainain is a mountain near the mountain of Uhud, and between it and Uhud there is a valley. I went out with the people for the battle. When the army aligned for the fight, Siba’ came out and said, ‘Is there any (Muslim) to accept my challenge to a duel?’
Hamza bin `Abdul Muttalib came out and said, ‘O Siba’. O Ibn Um Anmar, the one who circumcises other ladies! Do you challenge Allah and His Apostle?’ Then Hamza attacked and killed him, causing him to be non-extant like the bygone yesterday. I hid myself under a rock, and when he (i.e. Hamza) came near me, I threw my spear at him, driving it into his umbilicus so that it came out through his buttocks, causing him to die.
When all the people returned to Mecca, I too returned with them. I stayed in (Mecca) till Islam spread in it (i.e. Mecca). Then I left for Taif, and when the people (of Taif) sent their messengers to Allah’s Messenger, I was told that the Prophet did not harm the messengers; So I too went out with them till I reached Allah’s Messenger. When he saw me, he said, ‘Are you Wahshi?’ I said, ‘Yes.’ He said, ‘Was it you who killed Hamza?’
I replied, ‘What happened is what you have been told of.’ He said, ‘Can you hide your face from me?’ So I went out when Allah’s Messenger died, and Musailamah Al-Kadhdhab appeared (claiming to be a prophet). I said, ‘I will go out to Musailamah so that I may kill him, and make amends for killing Hamza.
So I went out with the people (to fight Musailamah and his followers) and then famous events took place concerning that battle. Suddenly I saw a man (i.e. Musailamah) standing near a gap in a wall.
He looked like an ash-colored camel and his hair was dishevelled. So I threw my spear at him, driving it into his chest in between his breasts till it passed out through his shoulders, and then an Ansari man attacked him and struck him on the head with a sword. `Abdullah bin `Umar said, ‘A slave girl on the roof of a house said: Alas! The chief of the believers (i.e. Musailamah) has been killed by a black slave.” – (Sahih al-Bukhari Volume 5, Book 59, Hadith 399)
Maulana Wahiduddin Khan
Wahsi ibn Harb, who had been responsible for the death of the Prophet’s uncle Hamzah. Realizing that the Muslims would kill him if they laid their hands on him, he fled from Makkah to Ta’if. Later on he came before the Prophet in Madinah, sought forgiveness for his crime and offered to accept Islam.
The Prophet admitted him into the fold of Islam and forgave him. He joined in the fight against the false prophet Musaylimah during the caliphate of Abu Bakr. It was he who finally slew Musaylimah, with the very same weapon that had made a martyr of Hamzah. 
Ṣafi al-Raḥman Mubarakfuri:
Hamza’s assassin, Wahsi bin Harb, described how he killed Hamzah. He said:
‘I was a slave working to Jubair bin Mut’im, whose paternal uncle Tu’aimah bin Adi was injured at Badr battle. So when Quraish marched to Uhud, Jubair said to me: ‘if you kill Hamzah, the uncle of Muhammad, stealthily you shall be manumitted.’
‘So I marched with the people to Uhud.’
He used to describe himself as,
‘I am a picaro good at spearing.’ ‘So when the two parties fought, I set out seeking Hamzah. I saw him amidst people fighting. He was like a white and black striped camel, striking severely with his word and no one could stand on his way.
By Allah! When I was getting ready and trying to seize the fit opportunity to spear him, hiding sometimes behind a tree or a rock hoping that he might draw nearer and be within ranger – at that moment I caught sight of Siba bin Abd Al-Uzza going closer towards him. When Hamzah observed him, he said: ‘Come on! O son of the clitoris-cutter,’ – for his mother used to be a circumciser.
Then he struck one strong stroke that could hardly miss his head. Wahsi said: ‘Then I balanced my spear and shook it till I was content with it, then I speared him and it went down into his stomach and issued out between his legs. He attempted moving towards me but he was overcome by his wound.
I left him there with the spear in his entrails till he died. Then I came to him, pulled out my spear and returned to the encampment place. I stayed there and did not go out, for he was the only one I sought. I only killed him to free myself. So as soon as I got back to Makkah, I became a free men.’ 
Among those destined to punishment was Wacksa, the Ethiopian, who had slain Hamza; but he had fled from Mecca on the entrance of the army. At a subsequent period he presented himself before the prophet, and made the profession of faith before he was recognized. He was forgiven, and made to relate the particulars of the death of Hamza;… 
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 Muhammad: A Prophet for All Humanity By Maulana Wahiduddin Khan page 331 – 332
 The Sealed Nectar Ar-Raheeq Al-Makhtum, Ṣafi al-Raḥman Mubarakfuri, page 261
 Mahomet and his successors – By Washington Irving, page 182