Sayyiduna Abu Musa (may Allah be pleased with him) said: Sayyiduna Mu'adh (may Allah be pleased with him) came to Yemen, and a Jew there had become a Muslim and then apostatised. When Sayyiduna Mu'adh (may Allah be pleased with him) came, he said: I will not dismount from my animal until I have him killed. So he was killed. One of the two narrators said: He had been asked to repent before that.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16882