Is charity accepted from one who is burdened with a large debt that he cannot repay until after a period of time, and he gives charity with water or with a very small amount, less than his debt? And is it permissible to fast with the intention of having a supplication answered?

If the debt is deferred, and charity does not affect its repayment, then there is no harm for the debtor in giving charity. However, if the debt is due, or if the charity affects its repayment, then it is not permissible for the debtor to give voluntary charity from what he needs to repay his debt, because repaying an obligatory debt takes precedence over a recommended voluntary charity. As for fasting with the intention of having a prayer answered, there is no harm in it. It is recommended for the needy person to fast, due to the hadith: "Three supplications are not rejected: the supplication of a father for his child, the supplication of a fasting person, and the supplication of a traveler."