Apostates - Sunnah.com - Sayings and Teachings of Prophet Muhammad (صلى الله عليه و سلم)
Narrated Abu Burda: Abu Musa said, "I came to the Prophet (ﷺ) along with two men (from the tribe) of Ash`ariyin, one on my right and the other on my left, while Allah's Messenger (ﷺ) was brushing his teeth (with a Siwak), and both men asked him for some employment. The Prophet (ﷺ) said, 'O Abu Musa (O `Abdullah bin Qais!).' I said, 'By Him Who sent you with the Truth, these two men did not tell me what was in their hearts and I did not feel (realize) that they were seeking employment.' As if I were looking now at his Siwak being drawn to a corner under his lips, and he said, 'We never (or, we do not) appoint for our affairs anyone who seeks to be employed. But O Abu Musa! (or `Abdullah bin Qais!) Go to Yemen.'" The Prophet then sent Mu`adh bin Jabal after him and when Mu`adh reached him, he spread out a cushion for him and requested him to get down (and sit on the cushion). Behold: There was a fettered man beside Abu Muisa. Mu`adh asked, "Who is this (man)?" Abu Muisa said, "He was a Jew and became a Muslim and then reverted back to Judaism." Then Abu Muisa requested Mu`adh to sit down but Mu`adh said, "I will not sit down till he has been killed. This is the judgment of Allah and His Apostle (for such cases) and repeated it thrice. Then Abu Musa ordered that the man be killed, and he was killed. Abu Musa added, "Then we discussed the night prayers and one of us said, 'I pray and sleep, and I hope that Allah will reward me for my sleep as well as for my prayers.'"
Narrated `Ali: Whenever I tell you a narration from Allah's Messenger (ﷺ), by Allah, I would rather fall down from the sky than ascribe a false statement to him, but if I tell you something between me and you (not a Hadith) then it was indeed a trick (i.e., I may say things just to cheat my enemy). No doubt I heard Allah's Apostle saying, "During the last days there will appear some young foolish people who will say the best words but their faith will not go beyond their throats (i.e. they will have no faith) and will go out from (leave) their religion as an arrow goes out of the game. So, where-ever you find them, kill them, for who-ever kills them shall have reward on the Day of Resurrection."