Musnad Ahmad 27:253

Yahya narrated to us, from Shu'bah, Simak ibn Harb narrated to me, from Mus'ab ibn Sa'd, that some people entered upon Ibn 'Amir during his illness and began to praise him. Ibn 'Umar said: "As for me, I am not the most deceitful of them to you. I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: 'Indeed, Allah, Blessed and Exalted is He, does not accept charity from spoils of war (taken dishonestly), nor prayer without purification.'"