The second opinion on this issue is that it is valid for one performing an obligatory prayer to pray behind one performing a voluntary prayer.

The evidence for this is as follows:

First: The general purport of the Prophet’s statement (peace and blessings be upon him): “The one most versed in the Book of Allah should lead the people in prayer” (1). The Prophet (peace and blessings be upon him) stipulated no condition other than this. Thus, the general wording indicates that if the imam is offering a voluntary prayer while the follower is offering an obligatory prayer, the prayer is valid.

Second: Mu'adh ibn Jabal would pray the night prayer with the Prophet (peace and blessings be upon him), then return to his people and lead them in that same prayer (2). It is known that the first prayer was obligatory and the second voluntary, and he was not reproved for doing so.

If someone were to say: Perhaps the Prophet (peace and blessings be upon him) did not know of this?

The response is from two perspectives:

First: If he did know, then that is precisely the point; and it is apparent that he did know, because Mu'adh ibn Jabal was complained about to the Messenger (peace and blessings be upon him) for making the prayer lengthy. It is not unlikely that the Messenger (peace and blessings be upon him) was told: “This man comes late, prays with you, then comes to us and makes the prayer lengthy for us.” Indeed, this is explicitly mentioned in Sahih Muslim: “Mu'adh prayed the night prayer with you, then came and began with Surat al-Baqarah …” (3).

Second: If we assume that the Prophet (peace and blessings be upon him) did not know, then Allah Most High certainly did know—