Invalidators of Prayer

In prayer, the underlying cause of invalidation is a lot of activity that does not belong to the prayer:

• Speaking in prayer, whether purposefully or forgetfully, invalidates it. An exception here is forgetfully saying the "assalam" saying during prayer.
• If the leader of the prayer recited Qur'aan by reading from a book (not merely reading)
• Entering another prayer by proscription (one has entered the other prayer)
• If someone said "there is no god but God" intending it as an answer to someone else, but not if he intended by it to make someone aware that he was praying.
• If someone helps in the reciting of someone other than the leader of the prayer he is in, then his prayer becomes invalid.
• If someone helps his own leader remember in his reciting, it does not invalidate his prayer, unless the leader has already gone to another aayah. He should not hurry in this.
• If someone sneezed, and someone who was praying said "raHimaka Allah" (bless you), then the latter's prayer is invalidated.
• The one who clears his throat, and pronounces letters in doing so, invalidates his prayer unless he is excused by being unable to prevent it (i.e. naturally or to be able to recite), just like sneezing or belching.
• If a person sighed, moaned or cried with letter-sounds in prayer, then it invalidates it unless it is because of remembering Paradise or Hell (not pain or adversity)
• More than two consecutive movements
• Killing scorpions or any type of snake during prayer is not harmful
• The one who eats or drinks in prayer invalidates it, whether it was intentionally or not.
• Exempted here is if you swallowed something that was already in your mouth before the prayer started and it was less that a chick-pea in size.
• To answer a greeting during prayer invalidates it, if it is by the tongue or by shaking hands. It is disliked if it is done by giving a sign (such as a nod.)