Is it permissible to pay off a father's debt from Zakat?

If the father incurred debt for maintenance, the son is not permitted to pay him zakat, because the father's maintenance is obligatory upon the son. However, if the debt was for a purpose other than maintenance, it is permissible to repay it from zakat, because repaying the father's debt is not obligatory upon the son. Based on what Ibn Baz and Ibn Uthaymeen mentioned, it is permissible for the son to pay his father's debt from his zakat if the father is unable to repay his debt, provided that the cause of the debt was not to acquire maintenance that is obligatory upon the son.