مسائل المنتخبه (Articles Of Islamic Acts) - الخوئي، السيد أبوالقاسم - الصفحة ٢٤٨ - ORDERS REGARDING THINGS WHICH INVALIDATE PRAYERS

In fact if he intentionally turns from the direction of Qibla to such an extent that the people do not say that he is facing Qibla his prayers will become void eventhough he may not turn fully towards the right or the left side.
١١٤٠. If a person turns his head intentionally, or by mistake to such an extent that he faces the right or left side of Qibla or turns more than that his prayers isvoid. However. if he turns his head only a little so that the people do not say that he has turned his face from Qibla - whether he does so intentionally or by mistake - hisprayers is not nullified. And it he turns his head so much that people may say that he has turned his face from Qibla but does not reach the right or left limit of Qibla hisprayers will be void if he has turned his face intentionally. but will be in order if he has turned his face by mistake.
Sixth The sixth thing, which invalidates prayers, is that one utters a word, consisting of one or more letters, intentionally, though it may carry no meaning.
١١٤١. If a person utters a word consisting of one or more letter by mistake, although that word may carry no meaning his prayers does not become invalid, but it isnecessary that after offering the prayers he should perform sajdatus sahu as will be explained later.
١١٤٢. There is no harm in coughing, belching or sighing during the prayers. However, uttering words like Oh or Ah intentionally makes the prayers invalid.
١١٤٣. If a person utters a word with the object of recitation e.g. he says Allahu Akbar with that intention and raises his voice while saying it in order to drawanother persons attention to something there is no harm in it. Rather, there is no harm if he says something with the intention of recitation, in order to bring something toanother persons knowledge.
١١٤٤. There is no harm in reciting the Quran (except the four verses Which make prostrations obligatory and which have