How should the master manage the earnings (Kasb) of his slave?

Primary text

The master has discretion either to provide sustenance from his own wealth and take all of the slave's earnings, or to allow the slave to use his earnings for his own sustenance, provided the earnings cover the needs, or to dedicate the earnings towards the service rendered. If the earnings are sufficient for sustenance and yield a surplus, the surplus belongs to the master. If the earnings are insufficient, the master is responsible for covering the remainder of the necessary provision.