In a narration of al-Tabarani the wording is: "Sayyiduna Abu Bakr (may Allah be pleased with him) said: 'If you kill them, they will enter Hellfire, and if you take ransom from them, (perhaps later on) they will become our supporters.' Sayyiduna Umar (may Allah be pleased with him) said: 'I think that you should bring them forward and then strike their necks, for these are the leaders of disbelief and the chiefs of disbelief. By Allah, they were not content with forcing us to leave, until they became the first of the Arabs to wage war against us.'"
This narration is muttasil (connected); its chain contains Musa bin Mutayr, and he is da'if (weak).