Al Nadr ibn al-Harith was an oppressor and tortured many Muslims in Mecca (Makkah). He persecuted Muslims. He was a criminal who had waged war against the Prophet and his community, so he was not as innocent as critics make him out to be. The following sources shed more light on this person Nadr (Nadir);
On their way back to Madinah, at a large sand hill, the Prophet (p) divided the spoils equally among the fighters after he had taken Al-Khums (one-fifth). When they reached As-safra, he ordered that two of the prisoners should be killed. They were An-Nadr Bin Al-Harith and Uqbah Bin Abi Muait, because they had persecuted the Muslims in Makkah, and harboured deep hatred towards Allah and His Messenger (p). In a nutshell, they were criminals of war in modern terminology, and they execution was an awesome lesson to oppressors. 
Nadhr (Nazr), one of the prisoners of war, was executed after the battle of Badr for his crime of severely tormenting Moslems at Mecca. Musab has distinctly reminded him of his torturing the companions of Mohammad, so there was nothing of a cruel and vindictive spirit of the Prophet displayed towards his enemies in the execution of Nazr as it is made out by Sir W. Muir. On the other hand, his execution is denied by some critics, like Ibn Manda and Abu Naeem, who say, that Nazr Ibn Haris was present at the battle of Honain, A. H. 8, six years after that of Badr, and was presented with one hundred camels by Mohammad. Sir W. Muir himself puts down very quietly Nadhir Ibn al-Harith’s name in a footnote (Vol. IV, page 151) as a recipient of one hundred camels at Honain. The same Nadhr-bin-Harith is shown among the earliest Moslem refugees who had fled to Abyssinia. These discrepancies leave no doubt that the story of Nadhr’s execution is not a fact. … 
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 Ar-Raheeq Al-Makhtum – The Sealed Nectar: Biograpghy of the Noble Prophet By Safi-Ur-Rahman al-Mubarakpuri, page 143 – 144
 A Critical Exposition of the Popular Jihad (Original 1885) – Cheragh Ali page 77 – 79