Is the Mukharajah valid if both the master and the slave agree to it?

Primary text

If the master and the slave mutually agree to the Mukharajah, it is permissible. Evidence for this is found in the report that Abu Dhabyah cupped the Prophet (peace be upon him), received his payment, and the Prophet commanded his masters to lighten the Mukharajah imposed upon him. It is reported that many Companions imposed a Mukharajah upon their slaves; for instance, Al-Zubayr had one thousand slaves, each charged one dirham daily.