How does a worshiper make up two days' worth of missed 'Isha prayers, and does he pray the Shaf' and Witr with them?

If a person intentionally abandons prayer, they have committed a grave sin. They must repent and, according to the majority of scholars, make up the prayers. However, if they missed the prayers due to an excuse, such as sleep or forgetfulness, there is no sin upon them. Many scholars hold that they must make them up immediately, and this is the more cautious approach. As for making up the Witr prayer, there is a difference of opinion, and the preponderant view is that it is legislated.