Is it permissible for a creditor to instruct his family not to collect a debt from a procrastinating debtor after his death?

If a man bequeaths that his family should not collect a debt from a certain person after his death, and the bequest is to absolve a debtor who is not an heir, then it is a valid bequest within the limits of one-third of the estate. However, if the debtor is one of the heirs, then the bequest to absolve his debt is forbidden by Sharia (definition), based on the Prophet's (peace and blessings be upon him) saying: "There is no bequest for an heir." It is also forbidden to bequeath more than one-third to a non-heir. Nevertheless, this forbidden bequest becomes valid if the heirs permit it.