Musannaf Ibn Abi Shayba 18:1222

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: ‘Uyaynah ibn ‘Abd al-Rahman narrated to us, from Abu Bakrah, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever kills a person under a covenant (mu’ahadah) without his due right, Allah has forbidden Paradise to him."