If the obligatory or obligatory prayers are missed, its qaza must be performed. If the sunnat or nafl prayers cannot be performed, the qasas do not have to be performed. There is no fixed time for performing qaza prayers. You have to read it whenever you remember and when the opportunity arises. But if you remember the forbidden times, you have to wait. The Prophet (peace and blessings of Allaah be upon him) said: It is not wrong for a person to perform the prayers unintentionally. However, it would be wrong to perform the prayers intentionally while awake. Therefore, when one of you forgets to perform the prayer, he should perform it as soon as he remembers, and the next day he should perform the prayer of that time at his appointed time. (Sunan Abu Dawood , Hadith Number: 436 Hadith Man: Sahih). The easiest way to perform qaza prayers is to perform qaza more than once during each prayer. For example, after the Azan of Zuhr prayers, a person performs Qaza prayers before performing the obligatory prayers of that day and then performs the prayers of that day. If one has missed more than one prayer, from which prayer will he start ? Muhammad ibn Bashar Bunder (R) narrates from Jabir ibn Abdillah (may Allah be pleased with him) that on the day of the trench war , Umar (may Allah be pleased with him) came and began to rebuke the infidel Quraish and said to the Messenger of Allah (may peace be upon him): O Messenger of Allah ! Even the sun was setting. The Prophet (peace and blessings of Allaah be upon him) said , ' By Allaah! I could not realize it. Jabir Radiyallahu Anhu said, "Then we landed at Buthan." The Prophet (peace and blessings of Allaah be upon him) also performed ablution. We also performed ablution. After the sun had set, the Prophet (peace and blessings of Allaah be upon him) offered the Asr prayer and then the Maghrib prayer. (Sunan Tirmidhi , Hadith Number: 180 Hadith Man: Sahih). Abdullah ibn Mas'ud (may Allah be pleased with him) narrated that the polytheists hindered the Prophet (peace and blessings of Allah be upon him) from praying four times during the trench warfare. Even some part of the night passed but he could not perform the prayer. Later he asked Bilal (may Allah be pleased with him) to give Azan. Bilal Radiyallahu Anh gave Iqamah with Azan. The Prophet (peace and blessings of Allaah be upon him) offered the Zuhr prayer. Then he gave the iqamah again and the Prophet (peace and blessings of Allaah be upon him) offered the Asr prayer. Then he gave the iqamah again and the Prophet (peace and blessings of Allaah be upon him) offered the Maghrib prayer. Then he gave the iqamah again and the Prophet (peace and blessings of Allaah be upon him) offered the Isha prayer. (Sunan Tirmidhi , Hadith Number: 169 Hadith Man: Hasan).