Is it obligatory for the congregant to observe a moment of tranquility after the opening Takbir (Takbirat al-Ihram) and before making Takbir for prostration or bowing, and is it necessary to recite something from Al-Fatiha or the opening supplication during this period to avoid intentional silence which might invalidate the prayer, and what should one do concerning past prayers performed in this manner, given the doubt about their validity?

The takbirat al-ihram must be completed while standing, then one may move to the rukn (pillar) the Imam is in, whether prostrating or bowing. In this case, the worshiper does not recite the opening supplication (du'a al-istiftah) or Surah Al-Fatihah. It is a condition for the latecomer (masbuq) who catches the Imam bowing that the takbirat al-ihram be uttered with all its letters while standing. If even one letter of it is uttered while not standing, his prayer as an obligatory one is not valid.