Is a verbal agreement between a lawyer and his client on a 35% share of the recovered amount permissible (halal) or forbidden (haram)?

If the lawyer is certain or highly presumes the righteousness of his client's case, there is no harm in taking on the case. Some scholars have permitted the fee to be a percentage of what is obtained through the case. This is similar to the view of Shaykh al-Islam Ibn Taymiyyah, who allowed the compensation to be a common share of what results from the work, and Ibn Qudamah's view allowing a "ju'alah" (a stipulated reward) with an unknown compensation if it does not prevent delivery, such as: "Whoever returns my runaway slave shall have half of him."