Sayyiduna Ibn Umar (may Allah be pleased with him) says: The Messenger of Allah (peace and blessings be upon him) went to visit one of his Companions who was ill, and I was with him (peace and blessings be upon him). He (peace and blessings be upon him) went in to him and found him praying on a piece of wood (leaning on it), placing his forehead on that wood. He (peace and blessings be upon him) gestured to him, so he put the wood aside and took hold of a pillow. At that, the Messenger of Allah (peace and blessings be upon him) said: "Leave that as well. If you are able to prostrate on the ground, then do so; otherwise, prostrate by gesturing, and make your prostration lower than your bowing."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13026
Tariq bin Shihab narrates that he met Ibn Umar (may Allah be pleased with them both) while he was on Hajj or Umrah, so I came to him and said: O Abu Abd al-Rahman, we are people of a land who rent out bare (uncultivated) land for dinars and dirhams. He said: "We dislike that; this is muhaqalah." I said: Then may we give the land for a third or a quarter (of the produce)? He said: "There is no harm in that; we used to do that."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13027