If a person mistakenly places his forehead on something higher than the place of his knees and toes by more than the height of four closed fingers, in the event that the height of the object is such that it cannot be said he is performing sajdah, he must raise his head and place it on something that is not higher than the height of four closed fingers.
If the height of the object is such that it can be said he is performing sajdah, in the event that he becomes aware of this after saying the obligatory dhikr, he can raise his head from sajdah and complete the prayer. However, if he becomes aware of this before saying the obligatory dhikr, he must slide his head from it and place it on something equal to or lower than the height of four closed fingers and then say the obligatory dhikr.
If it is not possible for him to slide his forehead in this manner, he can say the obligatory dhikr in the position that he is in and complete the prayer, and it is not necessary for him to perform the prayer again.