The Messenger of Allah ﷺ said, "Whoever kills a person under a covenant of protection without just cause, Allah will forbid him from even smelling the fragrance of Paradise."
قال رسول الله ﷺ: من قتل نفسا معاهدة بغير حلها حرم الله عليه الجنة أن يجد ريحها.
Nasai (4748), Ahmad (20383), (20397), Ibn Abu Asim in ad-Diyat (209), and Bayhaqi (9/205) reported it, and Ibn Hibban (4882) and Hakim (1/44) graded it sahih, all of them from the hadith of Yunus bin Ubayd, from Hakam bin Aaraj, from Ashath bin Tharmala, from Abu Bakra, and he mentioned it. Its chain is hasan.Ashath bin Tharmala, with the tha having a damma, followed by a sakin ra, then a mim with a damma, no one narrated from him except Hakam bin Aaraj, as stated explicitly by Ahmad, Ibn Hibban, Abu Hatim, and Abu Zura, except that Ibn Abu Hatim transmitted from Ibn Main his statement, "Yunus bin Ubayd narrates from him, a Basran, thiqa, well known."I say, the people of knowledge have stated explicitly that Ashath has only one hadith, which is this one, so how could he be well known? Likewise, the statement of Ibn Main, "Yunus bin Ubayd narrated from him," was not corroborated by anyone else. And Allah knows best what is correct.As for Ibn Hajar, he said, "Thiqa," and perhaps that was based on the statement of Ibn Main, but the correct view is that he is hasan al-hadith.The hadith of Abu Bakra has other routes besides the one I have mentioned, but what I have cited is the most sahih of them. Among them is what Abdul-Razzaq reported (10/462), and through his route Ahmad (20469) and Bayhaqi (13318) and others. He said, Mamar informed us, from Qatada or someone else, from Hasan, from Abu Bakra, who said, I heard the Prophet ﷺ say, "The fragrance of Paradise can be found from a distance of a hundred years' journey, and there is no servant who kills a soul under covenant without right except that Allah forbids Paradise to him."Hasan here is Hasan Basri, the well-known imam, who is a mudallis and has used ambiguous transmission wording (an'ana). Ibn Hibban (7382) and others reported from Yunus bin Ubayd, from Hasan, from Abu Bakra. Bukhari, Daraqutni, and others said, the hadith of Ashath is more sahih.