Whispering and Doubts in Prayer

Question :

I am often in doubt over how many Rak'ahs I have prayed, even when I recite aloud so that I may remember what I have recited, I am also seized with doubt. Then after I have completed the prayer, I feel as if I have forgotten a Rak'ah or a prostration or the sitting of Tashahhud. This is so in spite of the fact that I am very careful not to fall into doubt concerning my prayers, but without any benefit. Therefore, I request that you guide me to what I should do in the above-mentioned circumstances. Should I repeat the prayer when I am in doubt? And is there any supplication I can make at the start of the prayer in order to alleviate doubt?

Answer:

You must fight this whispering and take precautions against it, seeking refuge with Allah much from the accursed Satan, in accordance with the Words of Allah, the Most High:
Say: "I seek refuge with (Allah) the Lord of mankind, the King of mankind, the Ilah (God) of mankind, from the evil of the whisperer (the devil who whispers evil in the hearts of man) who withdraws (from his whispering in one's heart after one remembers Allah)."

And His Words:
And if an evil whisperer comes to you from Shaitan (Satan), then seek refuge with Allah. Verily, He is All- Hearing, All-Knowing.

And if you finish prayer or Wudhu' and you are then seized by doubt, then shun it and pay it no heed, and consider that your prayer or Wudhu' is correct. If the doubt occurs during the prayer over whether you have prayed three or four Rak'ahs, then assume that you have prayed three and complete the prayer. Then perform the two prostration of forgetfulness before making the Taslim, because the Prophet said that whoever was afflicted by forgetfulness such as this to do as we have said. May Allah protect us and you from Satan.

Source:
Ibn Baz
Fatawa Islamiyah, Vol. 2 Pages 271-272