Musannaf Ibn Abi Shayba 28:931

Waki' narrated to us, he said: Hammam narrated to us, from Qatadah, from Zurarah ibn Awfa, he said: A man came to Ibn Abbas and said: "I intended to go on a military expedition, but my parents are forbidding me." He said: "Obey your parents and stay, for the Byzantines will find someone other than you to fight them."