Musnad Ahmad 28:584

'Affan narrated to us, Shu'bah narrated to us, from Habib ibn Abi Thabit, [who said]: I heard Abu al-'Abbas—and he was a poet—say: I heard 'Abdullah ibn 'Amr say: A man came to the Messenger of Allah, may Allah bless him and grant him peace, and asked his permission for Jihad. He said: "Are your parents alive?" He said: "Yes." He said: "Then in them, strive [perform Jihad]."