Is it obligatory to make up missed prayers after repenting from abandoning them, and what is the expiation for this sin?

A person who abandons prayer must hasten to repent to Allah and renew their faith, because the preponderant opinion is that they have committed an act of disbelief. They must also make up for the prayers they missed as a precaution. If they know the number of missed prayers, they should perform them in order according to their ability. If they do not know the number, they should pray a number that absolves them of their obligation. Furthermore, they should increase their voluntary prayers and good deeds, attend scholarly gatherings, and avoid bad company.