Musnad Ahmad 28:335

Waki’ narrated to us, Mis’ar and Sufyan narrated to us, from Habib ibn Abi Thabit, from Abu al-Abbas al-Makki, from Abdullah ibn Amr, who said: A man came seeking permission from the Prophet, peace and blessings of Allah be upon him, for Jihad. The Prophet, peace and blessings of Allah be upon him, said to him: "Are your parents alive?" He said: "Yes." He said: "Then in them, strive [in Jihad]."