مسائل المنتخبه (Articles Of Islamic Acts) - الخوئي، السيد أبوالقاسم - الصفحة ٢٦٤ - DOUBTS WHICH ARE SOUND

(ix) If a person doubts while standing as to whether he has performed ٥ units or ٦ units he should sit down and recite tashahhud and salaam of the prayers. Thereafter he should perform two sajdatus sahv. In the foregoing four situations one should, on the basis of obligatory precaution, also offer two sajdatus sahv on account of undue qiyam.
١٢٠٩. In case a person has one of the above sound doubts he should not, on the basis of obligatory precaution, break the prayers, but act in accordance with theorders as detailed above.
١٢١٠. In case a person, while offering prayers, has one of the doubts for which offering of "Precautionary Prayers" is obligatory and he finishes the prayers theobligatory precaution is that he should offer "Precautionary Prayers" and unless he has offered it he should not offer the prayers again. And in case he offers the prayersagain before doing anything which nullifies prayers his second prayers will also be void. In case, however. he engages himself in prayers after having done something whichnullifies prayers his second prayers will be in order.
١٢١١. When a person has one of the doubts which nullifies the prayers and knows that on being transferred to the next act he will form a strong ground on acquirecertainty (i.e. if he gets engaged in the next ad of prayers his doubt will change into a strong opinion or belief) it is not permissible for him to continue the prayers inthe state of doubt. For example if he doubts while standing whether he has offered one unit or more, and knows that if he goes into bowing he will form a strong opinion orhave belief on one side, it is not permissible for him to perform bowing in this state.
١٢١٢. If initially the opinion of a person is stronger on one side and later both the sides become equal in his eyes he should act according to the orders regarding doubt. And if initially the two sides are equal in his eyes and he decides to act according to his obligation. and later his opinion moves to the other side,