Praise be to Allaah. It says in Fatawa al-Lajnah al-Daa’imah:
Making du’aa’ after the obligatory prayers is not Sunnah if it is done by raising the hands, whether that is done by the imam alone or a member of the congregation alone, or it is done by them both together.
Rather that is bid’ah, because it was not narrated that the Prophet (Sallallahu a’alaihi wa sallam) or any of his companions (may Allaah be pleased with them) did that.
With regard to making du’aa’ without doing that (raising the hands etc.), there is nothing wrong with it, because there are some ahaadeeth concerning that.
Fataawa al-Lajnah al-Daa’imah, 7/103
The Committee was asked about raising the hands for du’aa’ after the five daily prayers – is it proven that the Prophet (Sallallahu a’alaihi wa sallam) raised his hands or not? If it is not proven, is it permissible to raise the hands after the five daily prayers or not?
They replied: It is not proven that the Prophet (Sallallahu a’alaihi wa sallam) raised his hands in du’aa’ after the obligatory prayers as far as we know, so raising them after the salaam of an obligatory prayer is contrary to the Sunnah.
Fataawa al-Lajnah, 7/104
The Committee also stated that saying du’aa’ out loud after the five daily prayers or regular Sunnah prayers, or reciting du’aa’ in unison as a regular practice is a reprehensible innovation (bid’ah), because it was not proven that the Prophet (Sallallahu a’alaihi wa sallam) or his companions (may Allaah be pleased with them) did anything like that.
Whoever makes du’aa’ after the obligatory or regular Sunnah prayers in unison is going against the way of Ahl al-Sunnah wa’l-Jamaa’ah.
Fataawa Islamiyyah, 1/319
And Allaah knows best.