Hawzah News Agency – Believers who are incapable of performing the prostrations of the canonic prayers in their normal form (e.g. due to old age or physical impairment) typically sit on a chair and perform their prostrations by placing their heads on a table in front of them. First of all, does this count as a valid prostration? Second, how should they position the seven body parts integral to the validity of a proper prostration?

If those incapable of performing the prostration in its standard form can bend over and place their heads on a table in front of them, they should do so, and this would constitute the proper prostration for them. As regards the position of the seven body parts involved in prostration, they should as far as possible observe the proper position or the closest position thereto. As such, it is impermissible for those who can place their heads on a table in front of them to place the turbah on their forehead using their hands. But, obviously, they are absolved of the requirement to place their knees on the ground (as the assumption is that they have to be seated on a chair).

Source: https://www.leader.ir/en/book/32/Practical-Laws-of-Islam