Sahih Bukhari
Volume 4, Book 52, Number 260:
Ali burnt some people and this news reached Ibn 'Abbas, who said, "Had I been in his place I would not have burnt them, as the Prophet said, 'Don't punish (anybody) with Allah's Punishment.' No doubt, I would have killed them, for the Prophet said, 'If somebody (a Muslim) discards his religion, kill him.' "
Volume 9, Book 83, Number 37:
I said, "By Allah, Allah's Apostle never killed anyone except in one of the following three situations: (1) A person who killed somebody unjustly, was killed (in Qisas,) (2) a married person who committed illegal sexual intercourse and (3) a man who fought against Allah and His Apostle and deserted Islam and became an apostate."
Volume 9, Book 84, Number 57:
Some Zanadiqa (atheists) were brought to 'Ali and he burnt them. The news of this event, reached Ibn 'Abbas who said, "If I had been in his place, I would not have burnt them, as Allah's Apostle forbade it, saying, 'Do not punish anybody with Allah's punishment (fire).' I would have killed them according to the statement of Allah's Apostle, 'Whoever changed his Islamic religion, then kill him.'"
Volume 9, Book 89, Number 271:
A man embraced Islam and then reverted back to Judaism. Mu'adh bin Jabal came and saw the man with Abu Musa. Mu'adh asked, "What is wrong with this (man)?" Abu Musa replied, "He embraced Islam and then reverted back to Judaism." Mu'adh said, "I will not sit down unless you kill him (as it is) the verdict of Allah and His Apostle
Volume 9, Book 84, Number 58:
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.