Dought & clear, - What is to be said in the prostration of forgetfulness and the prostration of recitation?. - (Prostration when reading Qur’aan and Prostration of thanksgiving)

What should the worshipper say when he prostrates for forgetfulness in
prayer (sujood al-sahw)? And what should he say when he performs a
prostration as required in certain verses of the Qur'aan?.
Praise be to Allaah.
When performing the prostrations of forgetfulness and of recitation,
you should say the same as you say when you prostrate in prayer:
"Subhaana Rabbiy al-A'la (Glory be to my Lord Most High)." What is
obligatory is to say that once, and the least required in order to do
it perfectly is to sayit three times. It is mustahabb to make du'aa'
when prostrating,reciting whatever you can of the du'aa's prescribed
in sharee'ah, because the Prophet(peace and blessings of Allaah be
upon him) said: "When bowing glorify your Lord, and when prostrating
strive in making du'aa', for then you are more likely to receive an
answer."
And the Prophet(peace and blessings of Allaah be upon him) said: "The
closest that a person can be to his Lord is when heis prostrating, so
say a lot of du'aa'."
These two hadeeth wereboth narrated by Muslim in hisSaheeh. The
Prophet(peace and blessings of Allaah be upon him) often used to say
when bowing and prostrating: "Subhaanaka Allaahumma wa bi hamdika,
Allaahumma ighfir li(Glory be to You, O Allaah, and praise. O Allaah,
forgive me)." Agreed upon – from the hadeeth of 'Aa'ishah (may Allaah
be pleased with her). And he(peace and blessings of Allaah be upon
him) also used to say when bowing andprostrating: "Subbooh quddoos
Rabb ul-malaa'ikah wa'l-rooh(Glorified, Holy, Lord of the angels and
the Spirit [i.e., Jibreel]." Narrated by Muslim in hisSaheeh.
And Allaah is the Source of strength.
Al-Lajnah al-Daa'imah li'l-Buhooth al-'Ilmiyyah wa'l-Ifta', 6/443.