Dought & clear,- (description of the prayer) - It is not Sunnah to say du‘aa’ following an obligatory prayer, placing the right hand on the forehead.

There is a dua which is said by placing the right hand on the forehead
after farz namaz. I want to know the hadith related with this dua.
Praise be to Allaah.
What is proven from the Prophet (blessings and peace of Allah be upon
him) is that when he had finished praying, he would ask Allah for
forgiveness three times, then he would say: "Allaahumma anta as-salaam
wa minka al-salaam, tabaarakta yaa dhaa'l-jalaali wa'l-ikraam(O Allah,
You are as-Salaam (the One Who is free from all defects and
deficiencies) and from You is all peace, blessed are You, Possessor of
majesty and honour).
This is based on what has been explained previously in the answer to
question no. 104163
Secondly:
After searching we could not find any proof for the du'aa' mentioned
by the questioner that is said after the obligatory prayer when
placing the right hand on the forehead.
Shaykh Ibn Baaz (may Allah have mercy on him) was asked:
There are some people who, after finishing the prayer, put their hands
on their foreheads for a while and they say that this is Sunnah. Is
what they say correct?
He replied: There is no basis for that as far as we know. There is no
basis for placing the hands on the forehead after prayer.
FromFataawa Noor 'ala ad-Darb.
And Allah knows best.