Is it valid to stipulate that a Mukatab may not beg for charity?

Primary text

According to Ahmad, quoting Jabir ibn Abdullah: 'They are bound by their conditions. If you see him begging, forbid him. If he says he will not repeat it, do not revoke his Mukatabah for one instance.' The apparent meaning is that the stipulation is valid and binding. If he violates it once, he is not declared incapable, but if he violates it twice or more, the master may declare him incapable. The stipulation is valid based on the Prophet's saying: 'Muslims are bound by their conditions,' and because there is benefit and legitimate purpose in this: that he not be a burden on people nor eat from their charity and impurities.