How should the Sick person Purify Himself?
1. The Sick person is required to purify himself with water, performing ablution from minor impurity and Ghusl from major impurity.
2. If he is unable to purify himself using water, due to weakness or fear of increasing his illness, or delaying his recovery, then he may perform Tayammum.
3. The way to perform Tayammum is to strike the clean earth with his hands once, then wipe his whole face with them, then wipe his hands, one with the other.
4. If he is unable to purify himself, the another person should assist him in making the ablution, or performing the Tayammum.
5. If a certain part of the body which is to be purified is afflicted by a wound, he should wash it with water; but if washing it with water will cause harm to him, then he may wet his hand with water and then wipe over it. If wiping over it may also cause harm he may perform Tayammum for it.
6. If he has a severe fracture in any of his limbs, which is covered with a dressing or cast, he may wipe over it with water, instead of washing it, and it does not require Tayammum, because the wiping takes the place of washing.
7. It is permisable to make Tayammum using a wall, or anything else which is clean and contains dust. If the wall is covered with anything which is not from th earth such as paint, then one should not make Tayammum with it, unless there is dust over it.
8. If the Tayammum is not made on the earth or a wall or anything else containing dust, there is no objection to the collecting of dust in container or a hankerchief, in order to make Tayammum with it.
9. If a person performs Tayammum for prayer, and remains in a purified state until the time of the next prayer, then he may pray with the Tayammum he made before and he does not need to repeat it for the second prayer, since he remains purified and nothing has invalidated it.
10. The sick person is obliged to cleanse his body from all manner of impurity, but if he is unable to do so, he may pray as he is, and his prayer will be correct and he does not need to repeat it.
11 The sick person is required to pray in clean clothes, and if they became soiled, they must be cleaned or replaced with clean ones. If this is not possible, he may pray as he is, and his prayer will be correct and he does not need to repeat it.
12. The sick person is obliged to pray upon something clean and if it becomes soiled, he must wash it, change for something clean or cover it with something clean. If he is unable to do so, he may pray there, and his prayer will be correct and he does not need to repeat it.
13. It is not permissible for the invalid to delay the prayer due to his inability to achieve purification; rather, he should purify himself as much as he is able, then perform the prayer on time, even if there is some impurity on his body, his clothes or his place of prayer, which he is unable to remove.
Shaykh Muhammad bin Saalih al-`Uthaymeen
Fatawa Islamiyah, Vol. 2, p23-25, DARUSSALAM.