All of this is derived from this noble verse: “So fear Allah as much as you are able.” Thus, whoever is unable to bow should gesture for it while standing, and whoever is unable to prostrate should gesture for it while seated.

Question: If he is unable to prostrate only upon his forehead because it has wounds and he cannot place it on the ground, but he is able to use his hands and knees, what should he do?

Answer: We apply the principle: “So fear Allah as much as you are able” [al-Taghabun: 16]. He should place his hands on the ground and lower himself towards it as much as he is able, due to His saying, Most High: “So fear Allah as much as you are able.” As for the view of those scholars who say that, if he is unable to prostrate upon his forehead, he is not required to prostrate with the rest of his limbs, this is a weak view. For if we apply the noble verse, “So fear Allah as much as you are able,” it indicates that he must prostrate upon the ground with whatever limbs he is able to use. Thus, if he is able to prostrate upon his palms, he must do so.

If we suppose that he is entirely unable to prostrate—that is, he cannot bend his back at all—then he is not required to place his hands on the ground, because this would not approximate the posture of prostration. But if he is able to lower himself towards the ground until he resembles one who is prostrating, then he must prostrate and bring his forehead as close to the ground as he can.

Question: A sick man says: “If I go to the mosque, I will be unable to stand, because I arrive at the mosque exhausted and cannot stand. But if I pray in my home, I pray standing, because I have not become tired and have not undergone hardship. Moreover, the imam may perhaps prolong the prayer in a manner that is difficult for me,”