Musannaf Ibn Abi Shayba 13:2981

Abu Bakr narrated to us, he said: Abd al-Salam narrated to us, from Ata, who said: A man from among our companions had a debt owed to him by another man, but he denied it. Then, something of his (the debtor's) came into my possession. He came to me and asked me, and he asked our companions, and they said: "He should take it." I asked Ibn Mughaffal, and he said: "He should fulfill his trust and seek his right. If he has evidence, (he should use it), otherwise, he should make him swear an oath."