Whoever kills a person under covenant who has the protection of Allah and His Messenger has violated the protection of Allah

It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Beware! Whoever kills a mu'ahad who has the protection (covenant of safety) of Allah and of His Messenger has violated the protection of Allah; he will not even smell the fragrance of Paradise, although its fragrance reaches from a distance of seventy years (kharif)."
This hadith is sahih (authentic) on the condition of Imam Muslim.

It is narrated from Sayyiduna Zayd bin Khalid al-Juhani (may Allah be pleased with him) that on the day of Khaybar a man from among the Companions of the Prophet (peace and blessings be upon him) died. The people mentioned him to the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Pray the funeral prayer over your companion (that is, I will not pray it)." On hearing this, the people's faces changed (with fear and astonishment). He (peace and blessings be upon him) said: "This companion of yours committed treachery in the way of Allah (with the spoils of war)." We searched his belongings and found some beads of the Jews' necklaces that were not worth even two dirhams.
This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but most probably they did not record it.

It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that whenever the Messenger of Allah (peace and blessings be upon him) obtained spoils of war, he (peace and blessings be upon him) would order Sayyiduna Bilal (may Allah be pleased with him), and he would make an announcement among the people. The people would bring their spoils, and he (peace and blessings be upon him) would take out a fifth (khums) from it and distribute the rest. (Once) after this announcement, a man came with a halter made of hair and said: O Messenger of Allah, this is (from) what we obtained of the spoils (which I have now brought). He (peace and blessings be upon him) asked: "Did you hear Bilal's announcement made three times?" He said: Yes. He (peace and blessings be upon him) said: "Then what prevented you from bringing it?" He offered some excuse, so he (peace and blessings be upon him) said: "Now you yourself will bring it on the Day of Resurrection; I will never accept it from you now."
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.