it is preferable to recite the authentically reported formulae of Du`a' (supplication) between the two prostrations; however, the Salah is not nullified if a person adds to or removes from it.Second, repeating an act mistakenly, whether a person prays individually, or an Imam, or a Ma'mum (a person being led by an Imam in Prayer), does not invalidate the Salah. However, he should offer Sujud-ul-Sahw, if he is an Imam, offers prayer alone, or is a latecomer. If he is a Ma'mum and attends the Salah from the beginning, he does not have to perform Sujud-ul-Sahw for the Imam bears the responsibility. If he, for example, mistakenly repeats Ruku`(bowing) or Sujud, or repeats the recitation of Al-Fatihah, it does not necessitate performing Sujud-ul-Sahw.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.