Is it permissible to waive a debt owed by someone in exchange for them mentioning God one hundred times daily for three years, so as to increase their connection with God?

Scholarly opinions differ on the issue of charging for acts of obedience. While some Hanafis prohibit charging for the call to prayer (adhan), the iqamah, Hajj, imamate, and teaching the Qur'an and Fiqh, the Shafi'is permit charging for what is not a personal obligation (not عين) upon the hireling. Some Malikis permit charging for recommended acts (mandubat) of remembrance (dhikr) and recitation. Based on this, there is nothing to prevent the work the questioner intends to do with his indebted brother. We hope the questioner receives a reward similar to that of the worker himself, for being a guide to good.