The Prayer of You Both

Allah (swt) said: the duʿāʾ of both of you has been accepted. In the ayah before, who was making the duʿāʾ? Mūsā. But the following ayah says: qad ujībat daʿwatukumā — verily, the invocation of you both is accepted. So why does it say the two of you? The mufassirūn say that Mūsā was making the duʿāʾ and Hārūn was saying āmīn. That is the explanation the mufassirūn give; therefore the duʿāʾ was actually made by both. Even though Mūsā was the one saying it, Hārūn was saying āmīn.

And that is why, when we are in ṣalāh and the imam is making duʿāʾ, it is all of us making duʿāʾ together — because we say āmīn. And that is why we say āmīn after al-Fātiḥah. What is the duʿāʾ in al-Fātiḥah that we are saying āmīn for? Ihdinā al-ṣirāṭa al-mustaqīm — guide us to the straight path. So all of us say āmīn, which means: O Allah, accept.