Is it permissible for owners of wealth to exchange guarantees of capital among themselves with checks to release the Mudarib from guaranteeing the capital?

It is impermissible to stipulate a guarantee from the worker in a Mudarabah contract, because he is an entrusted party (amin) and is not liable except in cases of transgression (ta'addi) or negligence (tafrit). Stipulating a guarantee invalidates the Mudarabah. It is permissible for the capital provider (rabb al-mal) to take a check or a promissory note to document that he has provided funds, but he is not permitted to demand it back except in cases of transgression or negligence.