مسائل المنتخبه (Articles Of Islamic Acts) - الخوئي، السيد أبوالقاسم - الصفحة ٢٥١ - ORDERS REGARDING THINGS WHICH INVALIDATE PRAYERS

say salam to one, who is older than him.
١١٥٨. If two persons say salam to each other, each one of them should, on the basis of obligatory precaution, give reply to the salam of the other.
١١٥٩. When a person is not offering prayers he should give a better reply to the salam For example, when one says salmun alaykum the other should say salamunalaykum wa rahmatulah in reply.
Seventh The seventh thing which makes prayers void is to laugh intentionally with voice. In case, therefore, a person laughs intentionally, but without voice, or by mistakewith voice. what is apparent is that his prayers is not invalidated.
١١٦٠. If, in order to suppress his laughter, the condition of the person offering prayers changes e.g. his color becomes red, it is better for him to offer theprayers again
Eight One who intentionally weeps loudly in connection with worldly affairs, his prayers will be nullified. and the obligatory precaution is that he should not weep forworldly affairs even without voice. However, if he weeps. with or without voice, on account of fear of Allah or for the Hereafter there is no harm in it and in fact it is oneof the best acts which a person performs.
Ninth One who performs an act which may destroy the form of prayers (for example clapping ones hands or jumping), his prayers will be nullified, and it is immaterialwhether that act is done intentionally or by mistake. However. there is no harm in performing an act which does not change the form of prayers (for example making a sign withones hand).
١١٦١. If a person remains still during prayers for so long a time that people may not say that he is offering prayers, his prayers is invalidated.
١١٦٢. If a person performs an act during prayers or remains silent for some time and is in doubt whether or not his prayers