Musannaf Ibn Abi Shayba 13:2836

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Ali bin Salih, from Abd al-A’la bin Amir, from Muhammad bin al-Hanafiyyah, from Ali, he said: If the collateral is more than what it was pledged for, and it perishes, then it is [held] according to what is in it, because he is a trustee regarding the surplus. And if it is less than what it was pledged for, and it perishes, the pledger returns the surplus.