Everyone who follows an imam while performing prayer—the Jumu^ah Prayer or other prayers–must fulfill the following obligations:
The follower (ma’mum) must not be ahead of his imam in the standing position or in saying the opening Allahu akbar. The prayer of the follower is invalid if he says his opening Allahu akbar during that of the imam. Doing other actions at the same time as the imam in other parts of the prayer is disliked (makruh), with the exception of saying: “Amin ”.
It is unlawful (haram) for the follower (ma’mum) to precede the imam by one integral of action. One’s prayer is invalidated by inexcusably preceding the imam by two consecutive integrals of action, whether both are long or one is long and the other is short. Similarly, the ma’mum invalidates his prayer if he lags behind the imam by two integrals of action, despite an excuse. If the ma’mum stays behind to finish the Fatihah and during this time the imam has finished his ruku^ and two prostrations, and has sat for the tashahhud or stood up for the following rak^ah, then the ma’mum must stop reciting the Fatihah and be in unison with his imam. In addition to this, the ma’mum must perform a rak^ah after the closing salam of the imam. However, if the ma’mum finishes reciting the Fatihah before the imam has sat for the tashahhud or stood up for another rak^ah, then the ma’mum follows his own order until he catches up with the imam.
The follower must know the movements of his imam.
The follower must be with his imam in a mosque (masjid), or else within 300 cubits.
The follower must not have any barrier between him and the imam which prevents him from reaching the imam.
The follower must have the format of his prayer agree with the format of the imam’s prayer. For example, it is invalid for the performer of the daily obligatory prayer to follow the performer of the Funeral Prayer (Salatul-Janazah).
The follower must not disagree enormously with his imam in a recommended act (sunnah), like the sitting for the first tashahhud. If the imam does it or leaves it, then the ma’mum does it with the imam or stands up with him.
In the Jumu^ah Prayer, the follower must have the intention to follow the imam while saying the opening Allahu akbar, and in other prayers, before following the imam. If the ma’mum was performing the Jumu^ah Prayer without having the intention to follow the imam within the opening Allahu akbar, his prayer would be invalid. In other than the Jumu^ah Prayer, the intention to follow the imam must be in the heart before following the imam in his moves. Following the imam in his moves without the intention to follow invalidates the ma’mum’s prayer. However, if one’s moves agree with the imam’s moves accidentally and unintentionally, one does not invalidate one’s prayer.