If one of them challenges another to solve a riddle and gives him something if he solves it, does this fall under the category of *ju'alah* (reward for a specific task)?

Question:
Honorable Shaykh, may Allah grant you success. He says: If a man challenges another man to do something permissible, such as solving a riddle or solving a difficult problem, and he does it, does this fall under the category of *ju'alah* such that the other one is entitled to it?

Answer:
It falls under the category of racing, which is permissible only in the three cases specified by the Prophet (peace and blessings be upon him). However, Ibn al-Qayyim (may Allah have mercy on him) says that matters of knowledge and matters of jurisprudence fall under jihad in the cause of Allah, so it is permissible to take prizes for them, such as memorizing the Qur'an or memorizing hadiths; because seeking knowledge is part of jihad in the cause of Allah.