What is the ruling on one who doubts their prayer and wishes to repeat it?

If doubt arises after the completion of prayer, it is not to be considered. However, if doubt occurs during prayer regarding the number of rak'ahs or the performance of a pillar, then whoever performs that which he doubted, his prayer is valid. But if he does not perform it until he has said the tasleem and a long interval passes after the prayer, his prayer becomes invalid, because one who doubts performing the pillars during prayer is like one who has not performed them. Thus, if a worshipper intentionally omits a pillar, his prayer is invalidated. If he omits it forgetfully and then remembers it during the prayer, he should perform it. If he does not remember it until after finishing the prayer, then if a long interval has passed, he must repeat the prayer. If the interval has not been long, he builds upon it. The determination of a long or short interval is referred back to custom and common practice.