Musannaf Ibn Abi Shayba 13:3175

Abu Bakr narrated to us, he said: Abd al-Wahhab al-Thaqafi narrated to us, he said: Malik ibn Dinar claimed that a man asked Ata’ and said: "I was a young boy, and I acquired wealth from sources I do not like, and I desire repentance." He said: "Return it to its owners." He said: "I do not know them." He said: "Give it away in charity, and you will have the reward for that, though I do not know if you will be safe from its sin or not." He said: "And I asked Mujahid, and he said the same."