Assalaamu alaykum. I am an 18-year-old girl. When I pray, my knees get hurt. Then they turned darker than usual. Also, the top of my forehead became darker, which is known as 'zabebet l salah'. My question is: can I pray on my bed or put a thick cloth on the floor in order to avoid the harm?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

It is permissible for you to perform the prayer on the bed as long as the body parts that touch the ground during the prostration (hands, forehead, knees, and feet) are firmly established on that surface (meaning that if you press hard, they will not sink down any further). However, if you are prostrating on a material made of ruffled cotton or the like, then the prayer is invalid because one of the conditions for the validity of the prayer is that the body parts of prostration must be firmly established on the ground or surface on which the praying person is prostrating.

You may also put a thick material to prostrate on during the prayer as long as your forehead is firmly established on it, as we described above. It has been authentically reported that the Prophet, sallallaahu ʻalayhi wa sallam, used to prostrate on a khumrah (a small mat made of palm leaves that is big enough for the forehead). However, one should not prostrate on material attached to him, such as the clothes he is wearing, so as to avoid an issue subject to scholarly difference of opinion.

There is no problem with prostrating on material that is unattached to the praying person provided that the forehead is firmly placed on it as described above. This does not mean mere touching, as the scholars advised. An-Nawawi wrote:

“The most likely correct of the two views in this regard is that it is not sufficient for the forehead to merely touch the surface on which the praying person is prostrating; rather, his head must be firmly established on that surface, placing the weight of his head and neck on it so that the forehead is firmly established on it and not merely touching. If he is prostrating on cotton pad, straw, or an item stuffed with cotton or straw for example, then he should press his head hard against it during prostration until it flattens out and its impact would be found on a hand if it was placed beneath it; if he does not do so, then it is not sufficient for him as far as the prostration is concerned.” [Al-Majmoo’]

Allaah knows best.