Is the master permitted to prevent a slave from performing a voluntary fast?

Primary text

If a voluntary fast causes harm to the slave, the master has the right to prevent it because it causes the loss of the master's right by means of something not obligatory upon the slave. If the fast does not cause harm, the master cannot prevent it, as the slave is worshipping his Lord without detriment, resembling remembrance of Allah or performing voluntary prayers outside of service time.