Mukhtasar Muslim

Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) reports that the Messenger of Allah (peace and blessings be upon him) said: The boy whom Sayyiduna Khidr (peace be upon him) killed was born upon disbelief (meaning, he would have grown up to be a disbeliever), and if he had lived, he would have led his parents into rebellion and disbelief.