Sahih Bukhari Volume 4, Book 52, Hadith Number 270.
Narated By Jabir bin ‘Abdullah : The Prophet said, “Who is ready to kill Ka’b bin Al-Ashraf who has really hurt Allah and His Apostle?” Muhammad bin Maslama said, “O Allah’s Apostle! Do you like me to kill him?” He replied in the affirmative. So, Muhammad bin Maslama went to him (i.e. Ka’b) and said, “This person (i.e. the Prophet) has put us to task and asked us for charity.” Ka’b replied, “By Allah, you will get tired of him.” Muhammad said to him, “We have followed him, so we dislike to leave him till we see the end of his affair.” Muhammad bin Maslama went on talking to him in this way till he got the chance to kill him.