Supplication in Congregation after Prayer in Unison

Question :

In our village there are two congregations, each of them claims that it is following the right path. At the end of prayer, we find one group raising their hands and making supplication in unison in the following manner: "O Allah! Send prayers and blessings on Muhammad, Your slave and Your Messenger, the unlettered Prophet and upon his family and Companions and send the best salutations on him." And there is another supplication which they call Al-Fatih.

We find the other congregation saying, when the Imam makes the Taslim: "We will not do what the first congregation does."

When we ask the first congregation, they say that this supplication is from the completion of the prayer, and there is nothing in this supplication but goodness. As for the second congregation, they say that this supplication is an innovation which has not been reported from the Prophet and they cite as evidence the words of the Prophet:
"Whoever performs a deed which is not from this matter of ours, will have it rejected.

And there are other Hadiths which they cite as evidence. We young men do not know where the truth lies. We request from you, O brothers, to make clear for us who is right.

Answer:

We know of no basis for the practice of supplicating in congregation after the Imam's Taslim, in unison, which would prove its legality; and a Fatwa has already been issued from the Permanent Committee for Religious Research and Legal Rulings on this subject, the text of which is as follows:

"Congregational supplication after the obligatory prayers is not a Sunnah if it involves raising the hands, whether it be from the Imam alone or the one led in prayer alone or from both of them; in fact, it is an innovation, because it has not been transmitted from the Prophet, nor from his Companions, may Allah be pleased with them. As for supplication without raising the hands, there is no objection to it, because some Hadiths have been reported to that effect."

And through Allah is attained success. And may peace be upon our Prophet, Muhammad and upon his family and Companions.

Source:
The Permanent Committee
Fatawa Islamiyah, Vol. 2 Pages 261-262