Musannaf Ibn Abi Shaybah 34943 — What they said on a man who accepts

Abu Burdah (may Allah have mercy on him) said that Sayyiduna Abu Musa (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) sent me and Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) to Yemen. He (may Allah be pleased with him) said: One day Sayyiduna Mu'adh (may Allah be pleased with him) came to me, and with me was a Jew who had become a Muslim and then gone back from Islam to Judaism. At this he (may Allah be pleased with him) said: "I will not dismount at your place until you strike his neck."