Musannaf Ibn Abi Shayba 13:3105

Abu Bakr narrated to us, he said: Ibn Abi Za’idah narrated to us, from Ash’ath, from Muhammad, who said: A man established his evidence against another man, so his opponent said, "His oath is more beloved to me than his witnesses." So he asked him to take an oath, and he refused. Shurayh said, "How evil is that which you have praised your witnesses with," and he rejected their testimony. And Abdullah ibn Utbah said, "I will not give you a right that you will not swear an oath upon."