What is the reward for praying without any excuse?

There is half the reward for reading a copy

Question: What is the reward for praying without any excuse?

Answer: It is permissible to recite the prayer while sitting without any excuse, and in that case the reward will be half. The Messenger of Allaah (peace and blessings of Allaah be upon him) said:  The one who stands will get half the reward.  (Ibn Majah, Book of Prayer)