Sahih Muslim
The Book of Jihad and Expedition (Kitab Al-Jihad wal-Siyar)
Book Number: 019 / Hadith Number: 4334
Ibn Aun said: I wrote to Nafi' asking him about Nafl (spoils of war) and be wrote to me that Ibn 'Umar was among that expedition. (The rest of the hadith is the same.)