Musannaf Ibn Abi Shayba 28:260

Abu Usama narrated to us, he said: Jarir ibn Hazim narrated to us, he said: Qays ibn Sa’d narrated to me that ‘Ata’ used to say: If a man from the Muslims killed a man, then disbelieved and joined the polytheists and was among them, then returned repentant, his repentance from his polytheism would be accepted, and the retaliation (qisas) would be carried out upon him. And if he had joined the polytheists and did not kill, then disbelieved, then fought the Muslims, then was killed, then came repentant, it would be accepted from him and there would be nothing upon him.