Musnad Ahmad Hadith 22015

It is narrated from Burdah (may Allah be pleased with him) that Mu'adh bin Jabal (may Allah be pleased with him) arrived in Yemen to Abu Musa Ash'ari (may Allah be pleased with him). There he saw a man tied with ropes, so Mu'adh (may Allah be pleased with him) asked, "What is the matter with him?" They replied, "He was a Jew who accepted Islam, but later returned to his disliked religion and became a Jew again. We have been trying to bring him back to Islam for about two months." Mu'adh (may Allah be pleased with him) said, "I will not sit down until you kill him." So I killed him. Then he said, "The decision of Allah and His Messenger is that whoever turns back from his religion, kill him."