Musannaf Ibn Abi Shayba 13:3203

Abu Bakr narrated to us, he said: Qabisa narrated to us, he said: Harun al-Barbari narrated to us, he said: I asked al-Hakam and Hammad about a man who gave money to another man as a *mudaraba* (profit-sharing partnership) and called witnesses against him regarding it. Then the man came wanting to take his money from him, and he (the agent) said, "I have already returned it to you." Al-Hakam said: The burden of proof is upon him (the agent) that he returned it to him, just as he (the owner) had called witnesses against him regarding it. And Hammad said: He is to be believed regarding it, just as he is believed regarding the like of it.