Fathwa, - Assigning a supplication to every daily obligatory prayer

Question
Assalamu 'alaikum I read in a book about specific dua after each
prayer of fajr,dhuhr,asr etc.,but I havenot come across such dua
anywhere,so please tell me if it is correct to say these duas after
each prayer and if the Prophet)peace be upon him( said these.If we do
what was not taught by the Prophet,it would be rejected,right?pls
answer.May Allah reward you.
Answer
All perfect praise be to Allaah, The Lord of the Worlds. I testify
that there is none worthy of worship except Allaah, and that
Muhammadis His slave and Messenger.
There is nothing reported from the Prophetwith this meaning, and it is
not permissible to say these supplications as they are included in the
secondary innovations )i.e. the innovations where the basis of worship
is permitted but there is some change with regard to its reason, type,
amount, manner, time and place(, but if the meaning of these
supplications is good, and a praying person says them sometimes
without believing that they are a Sunnah, then this is permissible
because the supplication after performing obligatory prayers is, in
principle, among the legislated matters.
Allah Knows best.