Are the prayers in which a great deal of forgetfulness occurs and are compensated for by the prostration of forgetfulness valid, or must they be made up? And is it permissible to make up three prayers with one obligatory prayer?

A Muslim must make up missed prayers after repentance, whether they were omitted intentionally, out of ignorance, or forgetfulness. She should make up what she can daily, in a way that does not harm her body or livelihood, until she is reasonably sure that she has made up what was missed. She should not pay attention to obsessive doubts if they become frequent, and she is not required to perform the prostration of forgetfulness (sujood as-sahw).