Musannaf Ibn Abi Shayba 7:247

Abu Bakr narrated to us, he said: Umar ibn Ayyub narrated to us, from Ja’far ibn Burqan, from Maymun, from Shurayh: That a man entrusted him with wealth, and the ruler had a claim against that man at that time. He (the ruler) said to Shurayh, "We will make you take an oath." He said, "I used to defend his wealth as much as I could, as long as I was not forced to take an oath."