Answered by Shaykh Abdurrahman ibn Yusuf Mangera
I have a relative who spreads a Ja Nimaz (prayer mat) on the bed and prays on top of it (Ruku, Qayam, Sajda, everything) despite the fact that he is physically fit. He does not have any reason for not praying on the ground and praying on the bed … he just does it. What is the Islamic ruling regarding praying on a place where you sleep? Are factors such as doing Sajdah on a soft surface allowed? (Because I heard from some scholar that sajdah should only be performed on a hard surface and not a soft one.)
Assalamu alaykum
In the name of Allah the Inspirer of truth.
A condition for the validity of a sajda (prostrations) is that one is able to firmly set their forehead onto the ground or surface they are praying upon, and the head does not continue to sink down (see Tahtawi al-Maraqi 155). It would thus be difficult to perform a valid prostration on a bed unless the surface of the mattress is quite stiff and hard.
Aside from this, if it takes an effort to stabilize oneself while standing upon the bed, then that would be considered undesirable due to the loss of concentration in such a position.
And Allah knows best.
Wassalam,