Is it obligatory for the ma'mum to stand to the right of the imam?

Question : But is it obligatory or recommended?

Answer : Some scholars hold that it is obligatory, while others hold that it is recommended. Those who say it is obligatory argue that the Messenger (peace and blessings be upon him) moved Ibn 'Abbas from his left side to his right, and this is a movement in prayer. A movement in prayer does not occur except for an obligatory matter. Those who say it is recommended argue that this was not reported from the Messenger (peace and blessings be upon him) in his words, but only in his actions. The rule in the principles of jurisprudence is that the bare action of the Messenger (peace and blessings be upon him) indicates only recommendation. The fact that the Messenger moves does not make the matter obligatory, because movement is also permissible in a recommended act of prayer, and indeed recommended. Do you see, if the row is farther from you, do you say that the one who is farther is closer to the row, or do you move closer to the row? You move closer to the row, and yet that is a movement. So mere movement does not make the matter obligatory. However, there is no doubt that the precaution is for a person to adhere to this and stand to the right of the imam, in order to avoid scholarly disagreement.