The gravity of killing a believer

It is narrated from Sayyiduna Uqbah bin Malik (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "To proceed: what is the matter with a man who kills a man while he is saying, 'I am a Muslim'?" The killer said: O Messenger of Allah, he only said it to seek refuge (to save his life). The Messenger of Allah (peace and blessings be upon him) did like this (gesturing with his hands), disliked what he said, and turned his blessed face away from him, then said: "Allah has refused me (any leniency on behalf of) whoever kills a Muslim; Allah has refused me (any leniency on behalf of) whoever kills a Muslim."

It is narrated from Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "There are three things upon which I swear: Allah will not make the one who has a share (sahm) in Islam like the one who has no share in it; and the shares of Islam are fasting, prayer and charity. And the servant whose protecting friend Allah becomes, He will not hand him over to anyone else on the Day of Resurrection. And whatever people a man loves, Allah will bring him with them. And the fourth is such that, if I were to swear upon it, I hope I would not be sinful: whichever servant Allah conceals in this world, He will also conceal him in the Hereafter." Then Umar bin Abd al-Aziz (may Allah have mercy on him) said: When you hear a hadith like this which Urwah narrates from Sayyidah Aishah (may Allah be pleased with her), memorise it (well).
Imam Bukhari recorded from Shaybah al-Hadrami, and said in "al-Tarikh" that he is also called al-Khudri; he heard from Urwah and Umar bin Abd al-Aziz. This hadith has a sahih chain, but the two of them (the two Shaykhs) did not narrate it.

It is narrated from Sayyiduna Fadalah al-Laythi (may Allah be pleased with him), he says: I came to the Prophet (peace and blessings be upon him) and said: "I wish to accept Islam, so teach me some of the laws (rulings) of Islam." So he (peace and blessings be upon him) mentioned the prayer, the month of Ramadan and the times of the prayer. I said: "O Messenger of Allah! You are mentioning times in which I am busy, so teach me something comprehensive." So he (peace and blessings be upon him) said: "Even if you are busy, do not neglect the two 'Asrs ('Asrayn)." I asked: "What are the 'Asrayn?" For this was not the language of my people. He (peace and blessings be upon him) said: "Fajr and 'Asr."
This hadith is sahih (authentic) on the condition of Imam Muslim, but the two of them did not record it. It contains wordings which they did not record through another chain either, and the most beneficial of them is the mention of the laws of Islam, for that is in the narration of Abd al-Aziz bin Abi Rawwad from Alqamah bin Marthad from Yahya bin Ya'mar from Ibn Umar, which is not on the condition of either of them. And in this chain there is a divergence from Hushaym bin Bashir in his narration from Dawud bin Abi Hind which does not harm the hadith; rather, it strengthens it further.