Does a Muslim have to make up for all the prayers that he left without any excuse?

A Muslim is indeed required to make up for the prayers they have missed without a valid excuse. The concept of compensatory prayer, known as Qada, is supported by teachings from both Sunni and Shia traditions.

In the Shia tradition, it is narrated that Abu ‘Abd Allah, ‘Alayhi al-Salam, was asked about a man who has missed performing Salat (prayer) during the day. He responded, He can do whenever he wants. He can perform them after al-Maghrib or after al-‘Isha’. Al-Kafi 86:5561. This indicates flexibility in timing for making up missed prayers, highlighting that they should be performed as soon as the person is able.

Similarly, in the Sunni tradition, the Prophet ﷺ stated, If anyone forgets a prayer he should pray that prayer when he remembers it. There is no expiation except to pray the same. Sahih al-Bukhari 10:571. This reinforces the obligation of making up missed prayers, emphasizing that the only remedy for forgetting a prayer is to perform it at the earliest opportunity.

Both traditions agree that making up missed prayers is essential, and the guidance provided indicates that such prayers can be performed at various times, ensuring that the obligation can be fulfilled conveniently.