Prayer: Should I Pray Sitting at the Beginning of Time or Wait to Stand Later?

Practical Laws of Islam as per the teachings of Imam Khamenei

Prayer: Should I Pray Sitting at the Beginning of Time or Wait to Stand Later?

English:

Question #455:

I have been suffering from back pain for a long time which sometimes becomes so severe that it prevents me from praying while standing. Taking into consideration that if I want to perform my prayer at its beginning time, I will be compelled to do it in a sitting position, while if I wait, it may be possible for me to pray it at the end of its specific time in standing position, what is my duty in this situation?

Answer #455:

If there is a likelihood that you will be able to offer your prayer standing late in its time, it is an obligatory caution that you must wait until that time. But if you had performed your prayer sitting at the beginning of its time due to an excuse that continues until end of the time, your prayer is correct and you do not have to repeat it. However, if you are not able to pray in a standing position early during prayer time and you are sure that this excuse will continue until the time ends but it disappears and praying in standing position becomes possible before the time expiration, you are obliged to repeat your prayer standing.

-Imam Khamenei, Practical Laws of Islam, Importance and Conditions of Prayer