Whoever unjustly kills a person under a covenant, Allah forbids Paradise for him

It is narrated from Sayyiduna Abu Bakrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever unjustly kills a mu'ahad (a non-Muslim under a covenant of protection or granted refuge) will not even find the fragrance of Paradise, although its fragrance is perceived from a distance of five hundred years' travel."
This hadith is sahih (authentic) on the condition of Imam Muslim, but the two of them did not record it. We have found a supporting narration for Hammad bin Salamah in it:

Sayyiduna Abu Bakrah (may Allah be pleased with him) says: I heard the Messenger of Allah (peace and blessings be upon him) saying: "Whoever unjustly kills a mu'ahad, Allah will forbid him from smelling the fragrance of Paradise, although its fragrance is perceived from a distance of five hundred years' travel."

It is narrated from Sayyiduna Abu Bakrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever unjustly kills a mu'ahad, Allah has made Paradise forbidden for him."
Imam al-Hakim says: Our Shaykh Abu Ali al-Hafiz used to pass judgment based on the hadith of Yunus bin Ubayd from al-Hakam bin al-A'raj, but what the heart is content with is that this is an independent chain and that is another independent chain, and neither of them constitutes a defect ('illah) for the other, for Hammad bin Salamah is an imam, and Sharik bin al-Khattab also corroborated him, and he is a trustworthy Shaykh from al-Ahwaz. And Allah knows best.

It is narrated from Sayyiduna Alqamah bin Waqqas that there was a jester who used to go to the rulers and make them laugh with his talk. My grandfather (Alqamah) said to him: "Woe to you, O so-and-so! Why do you go to these people and make them laugh? For I heard Sayyiduna Bilal bin al-Harith al-Muzani (may Allah be pleased with him), the Companion of the Messenger of Allah (peace and blessings be upon him), narrating that the Messenger of Allah (peace and blessings be upon him) said: 'Indeed, a servant speaks a word pleasing to Allah which he does not even imagine will reach the degree it reaches, and Allah is pleased with him because of it until the day he meets Him. And indeed, a servant speaks a word displeasing to Allah which he does not even imagine will reach as far as it does, and Allah is displeased with him because of it until the day he meets Him.'"
This is a sahih (authentic) hadith. Imam Muslim used Muhammad bin Amr as evidence, and Sa'id bin Amir established its chain from him just as I mentioned above. It was likewise narrated by Sufyan al-Thawri, Isma'il bin Ja'far, Abd al-Aziz al-Darawardi, Muhammad bin Bishr al-Abdi and others. As for the hadith of al-Thawri:

It is narrated from Sayyiduna Bilal bin al-Harith al-Muzani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Indeed, a man speaks a word displeasing to Allah without realising how far it will reach, and because of it Allah records His displeasure (for him) until the Day of Resurrection. And indeed, a man speaks a word pleasing to Allah without knowing how far it will reach, and because of it Allah records His pleasure (for him) until the Day of Resurrection."

It is narrated from Sayyiduna Bilal bin al-Harith al-Muzani (may Allah be pleased with him) that he heard the Prophet (peace and blessings be upon him) saying: "One of you speaks a word pleasing to Allah which he does not even imagine will reach so far, and because of it Allah records His pleasure (for him) until the day he meets Him. And one of you speaks a word displeasing to Allah which he does not imagine will reach so far, and because of it Allah records His displeasure (against him) until the day he meets Him."

It is narrated from Sayyiduna Bilal bin al-Harith (may Allah be pleased with him) that he heard the Prophet (peace and blessings be upon him) saying: "Indeed, one of you says a word pleasing to Allah which he does not imagine will reach so far, and because of it Allah records His good pleasure for him until the day he meets Him. And one of you says a word displeasing to Allah which he does not imagine will reach so far, and because of it Allah records His displeasure for him until the day he meets Him."

It is narrated from Sayyiduna Alqamah bin Waqqas (may Allah be pleased with him) that a man of standing passed by him while he was in the market of Madinah and greeted him. Alqamah said to him: "O so-and-so! You have ties of kinship (with us) and a right as well, and I see that you go to these rulers and speak before them whatever Allah wills you to speak. Yet I heard Sayyiduna Bilal bin al-Harith al-Muzani (may Allah be pleased with him), the Companion of the Messenger of Allah (peace and blessings be upon him), saying that the Messenger of Allah (peace and blessings be upon him) said: 'Indeed, one of you speaks a word pleasing to Allah which he does not even imagine will reach so far, and because of it Allah records His good pleasure for him until the day he meets Him. And one of you speaks a word displeasing to Allah which he does not imagine will reach so far, and because of it Allah records His displeasure against him until the day he meets Him.'" Alqamah said (advising him): "Woe to you! Look at what you are saying and what you speak about, for many a time what I heard from Bilal bin al-Harith has prevented me from speaking (much)."
Imam Malik bin Anas abridged the narration of this hadith from Muhammad bin Amr and did not mention Alqamah bin Waqqas.