What is the ruling on holding a religious competition on WhatsApp for the fastest answer, with a recharge card given to the winner?

There is no objection to organizing beneficial competitions aimed at serving Muslims and providing them with knowledge. If a competition includes a prize, it is only permissible in matters explicitly stated by the Sharia, and what is appended to that—according to the most preponderant opinion—such as competitions for the Quran, Hadith, Fiqh, and what aids in spreading the religion; because this is a form of moral jihad.