بسم الله الرحمن الرحیم
Rulings Regarding Prayer- Qiyām- part 4
If one falls sick and is unable to perform prayer while standing, but they think they will probably be able to perform their prayer standing by the end of prayer time, based on obligatory precaution they must wait until they manage to perform their prayer in standing position.
However, if one cannot finally perform the entire prayer while standing, they should perform it in standing position as much as they can even by leaning on something like a crutch, but if they cannot keep on standing through the prayer, they should perform the rest of the prayer sitting and if they could not keep on praying while sitting either, they perform the rest of the prayer in lying position.
However, whenever they become able to sit up again or even stand up they must do so, but they must not recite the dhikrs of prayer while moving.
Sometimes, worshippers might be able to perform prayers in standing position, but based on rational probability they consider it likely that standing be detrimental to their body or that it prolongs their illness. In that case they should not perform prayers standing, but rather they can sit down.