While a woman prays, to what extent of uncovering her arms and wrists invalidate the prayer?

While a woman prays, to what extent of uncovering her arms and wrists invalidate the prayer?

Dear Brother / Sister,

Uncovering less than 1/4 of  a body part which needs to be covered does not invalidate the prayer. However, any uncovering which is more than 1/4 is an obstacle for the prayer. If a part of awrah is uncovered during the prayer and it is covered without any delay, the prayer is not invalidated. However, if it is uncovered in the length of rukn (part) of the prayer, that is, covered after waiting long enough to say "subhanallah" three times, the prayer is invalidated. The deed of covering should be performed with one hand. Things that are performed with two hands are regarded to be amal kathir (major action) and they invalidate the prayer.

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