The ruling on the prostration of Surat Sad in prayer and outside of it

Question:
Some scholars said: The prostration of Surat Sad is a prostration of gratitude that is performed outside of prayer, and if one prostrates inside the prayer, it becomes invalid. Is this correct?

Answer:
Yes, the prostration of Sad is a prostration of gratitude, without doubt. But whoever distinguishes between the prayer and outside of it, his statement is not correct. Rather, the correct view is that it is performed in the prayer and outside of it. And whoever says it is not performed in the prayer has erred. The Prophet (peace and blessings be upon him) prayed in Sad and prostrated in it while he was on the pulpit, (peace and blessings be upon him).
So whoever recites it, it is a recommended practice for him to prostrate, whether he is in the obligatory prayer, in the tarawih prayer, or outside of the prayer. It is a recommended practice for him to prostrate absolutely, even in the prayer. And whoever says that it invalidates the prayer, that is an erroneous statement with no basis in the Shari'ah at all.