It is reported from Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "When a man holds another man so that a third person kills him, the killer will be killed in retaliation and the one who held him will be imprisoned."
The Shaykh said: This narration is not mahfuz (preserved).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16029
Isma'il bin Umayyah said: The Messenger of Allah (peace and blessings be upon him) gave a judgement concerning a man whom one person held so that another could kill him, and he was killed: "The killer is to be killed and the one who held him is to be imprisoned."
A similar judgement is also reported from Ali (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16030
Isma'il bin Umayyah (may Allah have mercy on him) narrates in marfu' form: "Kill the killer and imprison the one who held (the victim)."
Abu Ubayd (may Allah have mercy on him) said: I heard Abdullah bin al-Mubarak (may Allah have mercy on him) narrating from Ma'mar (may Allah have mercy on him), from Isma'il bin Umayyah (may Allah have mercy on him), in marfu' form: "Imprison the one who held (the victim)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16031