Sahih Bukhari Volume 3, Book 45, Hadith Number 687.
Narated By Jabir bin ‘Abdullah : Allah’s Apostle said, “Who would kill Ka’b bin Al-Ashraf as he has harmed Allah and His Apostle ?” Muhammad bin Maslama (got up and) said, “I will kill him.” So, Muhammad bin Maslama went to Ka’b and said, “I want a loan of one or two Wasqs of food grains.” Ka’b said, “Mortgage your women to me.” Muhammad bin Maslama said, “How can we mortgage our women, and you are the most handsome among the Arabs?” He said, “Then mortgage your sons to me.” Muhammad said, “How can we mortgage our sons, as the people will abuse them for being mortgaged for one or two Wasqs of food grains? It is shameful for us. But we will mortgage our arms to you.” So, Muhammad bin Maslama promised him that he would come to him next time. They (Muhammad bin Maslama and his companions came to him as promised and murdered him. Then they went to the Prophet and told him about it.