Praise be to Allaah.
It is permissible to prostrate on soft surfaces like blankets
etc., so long as the worshipper can place his forehead and nose firmly on
the surface when prostrating. What is not allowed is prostrating on
something too soft, in which the worshipper’s face will sink and not be
Ibn al-Hamaam said in Fath al-Qadeer (1/304): It is
permissible to prostrate on grass, straw and cotton, if it is firmly laid on
the ground, and likewise compacted snow, but not if his face will sink into
it or it is not firmly laid on the ground. End quote.
Ibn al-Qayyim said in al-Bahr al-Raa’iq (1/337): The
basic principle is that just as it is permitted to prostrate on the ground,
it is also permitted to prostrate on anything that is like the ground, where
his forehead may be firmly placed, meaning that if he presses hard, his head
will not sink any further down. End quote.
Based on this, there is nothing wrong with prostrating on an
item like a blanket or mattress, if it is firm and will remain stable no
matter how much pressure a person puts on it.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was
asked about the ruling on prostrating on a sponge pad. He replied: If the
sponge is thin and will flatten out when he prostrates, then there is
nothing wrong with it.
Fataawa Ibn ‘Uthaymeen
And Allaah knows best.