What is the ruling on money saved from work that relies on giving money and gifts to doctors in exchange for prescribing a specific product, and is it permissible to use this money for marriage after repentance, and how does one expiate for this action?

It is not permissible to give money or gifts to doctors for prescribing a specific medicine, as this is a forbidden bribe. As for the salary earned from a mixed (permissible and forbidden) work, what was taken from it before knowing of its prohibition is not blameworthy. However, what was taken after knowing of its prohibition must be disposed of by giving it to the poor and needy, or for public welfare, and this is estimated by the proportion of the forbidden work to the total work. It is permissible to benefit from ill-gotten wealth to the extent of necessity for someone who finds no other lawful means, such as if he is poor, or needs to marry, or needs capital for a permissible business.