What is the maximum term of imprisonment as a ta'zir (discretionary) punishment?

"We have not found a limit for the duration of imprisonment. It appears to be according to the discretion of the ruler, because imprisonment is a disciplinary punishment (ta'zir), and ta'zir is left to the judgment of the Imam according to what serves the public interest. There is nothing in Islamic law that prevents the ta'zir punishment for the crime of murder from being execution or life imprisonment. As for ta'zir with more than ten lashes, the majority of scholars hold that it is permissible to exceed this number according to the discretion of the ruler and what he deems to be in the public interest."