1. In order to make his prayer valid, the follower, to begin with, has to express the intention, whether 
verbally or mentally, to the effect that he is going to offer his prayer under the leadership of the Imam.

2. The follower has to stand behind the Imam, or in the case of a single follower, beside the Imam, for if he stands ahead of the Imam even with his heels a bit ahead of his, the prayer will have no effect at all.

3. The follower has to follow and obey the Imam in all the articles, both Fard and Wajib, of the prayer. In the case of the Sunnat parts, however, it is not necessary to follow him strictly. For instance if the Imam is an adherent of Imam Shafi'i's school of thought and raises his hands to his ears while bending down for ruku, the Hanafite follower may not follow him in this. Similarly, if a Shafi'ite Imam recites the Qunut of the Fajr prayer, the Hanafite follower may not do so. In the Witr prayer however, if the Shafi'ite Imam recites the Qunut after performing ruku, the Hanafite follower also has to do the same for the recitation of the Qunut is an essential part of the Witr prayer. 

4. If in a congregational prayer, there is a single follower, whether an adult male or a boy, he should stand beside the Imam on his right with his heels a little behind the Imam's, for it is undesirable for the single follower to stand behind the Imam or on his left. However, if the single follower is a woman, she invariably has to stand behind the Imam.

5. It is undesirable for the follower to stand in the second or a subsequent row if there is room for him in the front row. If there is room for him in the front row, he should not stand alone,⁽¹⁾

but should pull back a follower from the front row (of whom he is sure that he would easily fall back and would not mind it). If there is no such person present in the front row, one may in the last resort stand alone at the rear.

6. The follower has to follow the Imam in all the articles of the prayer except recitation. If he does not perform any article, for instance ruku, with the Imam, or performs it late after the Imam has already performed it, his prayer will not be valid. However if the follower bends down in ruku a bit early or a bit late and joins the Imam in its performance, his prayer will be in order and valid. 

The Muqtadis (followers in prayer) can be of three kinds depending on the stage when they join the congregation: (a) Mudrak (b) Masbuq (c) Lahiq

(a) Mudrak : The Mudrak is the follower who joins the congregation from the very beginning and remains with the Imam throughout the prayer till the end.

(b) Masbuq : He is the follower who joins the congregation after one or more rak'ahs have been performed.

(c) Lahiq : He is the follower who joins the congregation from the beginning, but then loses one or more rak'ahs due to the breaking of wudu, or going to sleep, or the occurrence of Hadith Akbar (major impurity), or is unable to perform ruku or Sajdah Sahv due to an unusual rush of the people.

Regulations Concerning Masbuq

The Masbuq after joining the congregation has to perform the remaining prayer with the Imam. After the Imam has pronounced salutation and brought the prayer to an end, the Masbuq should stand up in complete his missed rak'ahs independently, in the following way:

1. First of all he should complete those rak'ahs in which recitation of the additional passage is necessary and then those in which it is not necessary.

2. He should sit in Qadah keeping in mind the rak'ah or rak'ahs that he has performed with the Imam. For instance, a person who joins the congregation during the Zuhr prayer, after three rak'ahs have been performed, should stand up after observing one (the fourth) rak'ah behind the Imam and then complete the remaining three rak'ahs independently as follows:

(a) He should start with al Fateha, recite an additional passage and sit in the first Qadah after Sajdah to complete two rak'ahs (the first being the one he has observed with the Imam).

(b) he should stand up after reciting Tashahhud in the usual manner and begin his third rak'ah with al Fateha which is to be followed by an additional passage, but should not sit in the Qadah.

(c) In the last rak'ah he should only recite al Fateha and sit in the final Qadah and complete his prayer in the usual way.

The Lahiq should first of all complete those rak'ahs which he has missed, like a follower quietly, i.e. without recitation and without even performing Sajdah Sahv in the case of a mistake. After completing the missed rak'ahs, he should join the congregation and complete the remaining prayer with the Imam. If the Imam in the meantime has completed the prayer, the Lahiq should complete his prayer independently.

For instance, a person starts his prayer with the Imam, but after performing one rak'ah his wudu breaks. In the meantime if the Imam has completed the second rak'ah also, the Lahiq should first perform his rak'ah independently in a separate place like a follower, and then re-join the congregation. If in the meantime, the Imam has completed the whole prayer, the Lahiq should complete his prayer independently in the usual way.

1.  According to Hadrat Wabisah bin Ma'bud, the holy Prophet saw a man offering his prayer alone at the rear of the congregation, and offered him to repeat his prayer (Tirmidhi, Abu Da'ud)

Everyday Fiqh (Vol.1) by Abdul Aziz Kamal ©1986 published by Islamic Publications (Pvt.) Ltd., 13-E Shah Alam Market, Lahore, Pakistan