Answered by Ustadh Sufyan Qufi
I didn’t know what to do when I doubted how many times I said “Subhana Rabi al-A’la,” so I prayed again. Was my prayer valid?
Yes, your prayer is valid despite forgetting how many times you said “Subhana Rabi al-A’la.” [Shurunbuli, Nur al-Idah]
This is because you have fulfilled all the integrals (standing, reciting Quran, prostration, etc.) and conditions (ritual purity, facing the qibla, covering your nudity, etc.) of the prayer. These are the only actions needed to pray a valid prayer.
If you don’t know them I urge you to take this course:
On Worship (Purification, Prayer, Fasting, Zakat, and Hajj): Shurunbulali’s Ascent to Felicity
Saying “Subhana Rabi al-A’la” during the prostration is not a part of the integrals and conditions of the prayer. Even not saying it at all won’t invalidate your prayer.
Nonetheless, it remains sunna to say “Subhana Rabi al-A’la” three times during each prostration. You will be rewarded for doing so; failing to do so regularly is sinful. [Shurunbuli, Nur al-Idah]
Please also remember that the number three is not a must. In fact, saying these clarifications three times is simply the minimum to reach the reward of the sunna in this matter. [Tahtawi, Sharh ‘ala Maraqi al-Falah]
The Messenger of Allah (peace and blessings be upon him) said: “When you prostrate, say: “Subhana Rabi al-A’la” three times. And this is the minimum.” [Muslim]
Thus if you were to say it more than three times, your reward would be greater. Just keep in mind to say it an odd number of times (such as three, five, seven, or nine times) because the Messenger of Allah (Allah bless him and give him peace) said: “Allah loves that which is odd.” [Bukhari] [Tahtawi, Sharh ‘ala Maraqi al-Falah]
And Allah knows best.
[Ustadh] Sufyan Qufi