Musannaf Ibn Abi Shayba 18:1220

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Yunus, from al-Hakam ibn al-A’raj, from al-Ash’ath ibn Tharmala, from Abu Bakra, he said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever kills a soul under a covenant (mu’ahada) without its right, Allah has forbidden Paradise for him, that he should smell its fragrance."