Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them), he says: The Prophet (peace and blessings of Allah be upon him) went out to visit a sick person, and I was with him. When he reached him, (he saw that) he was praying on a piece of wood and (while prostrating) he was placing his forehead on it. The Prophet (peace and blessings of Allah be upon him) gestured towards it and threw the wood away. He then took a cushion, and the Prophet (peace and blessings of Allah be upon him) said: "Remove it. If you have the strength to prostrate on the ground, then fine; otherwise, pray by making gestures, and bow lower for prostration than for bowing."