Wasn't that Abdullah Sarh :
From Ali Dashti's "23 Years, A study of the prophetic career of Muhammad", page 98.
"The last man named [in the list of people to be killed] had been one of the scribes employed at Medina to write down the 'revelations'. On a number of occassions, with Muhammad's consent, he changed the closing words of verses. For example, when Muhammad said "And God is mighty and wise", Abdullah Sarh suggested 'knowing and wise', and the prophet answered that there was no objection. Having observed a succession of changes of this type, Abdullah renounced Islam on the ground that the revelations, if from God, could not be changed at the prompting of a scribe such as himself. After his apostasy, he went to Mecca and joined the Qorayshites."
So you see the background behind the order to murder Abdullah. He was a threat to the credibility of the Qur'an. He was a Muslim, worked with Muhammad in writing down the Qur'an, and, from time to time he suggested some minor changes. Finally Abdullah realized that if this were truly from God, no changes would be made at the suggestion of a mere scribe. So, he realized Islam was false, and went back to Mecca. After Muhammad took Mecca, and issued the order to kill him, he hid out with Uthman who was one of Muhammad's closest companions. Later Abdullah pled for amnesty. Muhammad wanted one of his men to kill him on the spot, but they didn't know, because they couldn't read Muhammad's mind. So, finally Muhammad gave him amnesty.
http://www.answering-islam.org/Muhammad/Enemies/meccan10.html