you are able.” (1)
Thus, if it so happens that one of his hands is injured and he cannot prostrate upon it, then let him prostrate upon the remaining body parts, for Allah Most High says: “So fear Allah as much as you are able.” [Al-Taghabun: 16] Likewise, if he has undergone an operation on his eyes and is told, “Do not prostrate on the ground,” then he should gesture as much as he can and place whatever prostrating body parts he is able to place.
As for the statement of some jurists that whoever is unable to prostrate with his forehead is not required to do so with the rest of his body parts (2), this is accepted in certain cases: namely, when he is unable to bend down such that he would be closer to a complete prostration than to a fully upright posture. Such a person is not required to prostrate. But if he can gesture in such a way that he is closer to complete prostration than to sitting fully upright, then he must prostrate with the remaining body parts: he should lower himself towards the ground as much as he can, then place his hands.
If someone asks: What is the evidence for this?
The answer is that the evidence is that we have been commanded to prostrate and commanded to fear Allah as much as we are able. Therefore, if we are able to come closer to complete prostration, then we must come closer, because we would be like one in the posture of a prostrating person who has raised his forehead. But if we are unable to lower ourselves towards the ground such that we would be closer to prostration, then our obligation in that case is to gesture. Thus, one gestures, and is not required to place one’s hands or knees upon the ground.
The wisdom behind prostration is that it is part of perfect worship of Allah and humble submission to Him,