Musannaf Ibn Abi Shayba 37:515

Al-Fadl ibn Dukayn narrated to us, he said: Ja’far ibn Burqan informed us, from Rashid al-Azraq, from ‘Uqbah ibn Nafi’, he said: I asked Ibn ‘Umar: "With whom should I fight?" He said: "With those who fight for the sake of Allah, and do not fight with those who fight for the sake of this dinar and dirham."