Sayyiduna Abdullah bin Ja'far (may Allah be pleased with them both) said: One day I rode behind the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) told me something in confidence which I will not narrate to anyone. And what the Messenger of Allah (peace and blessings be upon him) most loved to screen himself with when relieving himself was a mound (a rock or the like) or a grove of date palms.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 446
Sayyiduna Jabir (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) went to relieve himself, and I followed him (peace and blessings be upon him) with a vessel of water. The Messenger of Allah (peace and blessings be upon him) looked, but the Messenger of Allah (peace and blessings be upon him) did not see anything behind which to screen himself. There were two trees at the edge of the valley. The Messenger of Allah (peace and blessings be upon him) went to one of them, took hold of one of its branches and said: "Submit to me by the command of Allah." So it submitted and went along with him (peace and blessings be upon him) like a docile camel that follows its leader, until he (peace and blessings be upon him) came to the other tree, took hold of one of its branches and said: "Submit to me by the command of Allah." And it too submitted in the same way. Joining the two of them, he (peace and blessings be upon him) said to them: "Join together over me by the command of Allah." So the two of them joined together. Sayyiduna Jabir (may Allah be pleased with him) said: I sat talking to myself, and when I glanced, suddenly the Messenger of Allah (peace and blessings be upon him) was before me, and the trees had separated, each standing in its own place.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 447
Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him): "Whoever goes to relieve himself should screen himself. If he finds nothing, let him gather a heap of sand and then turn his back to it, for the devils play with the private parts of the children of Adam. Whoever does so has done well, and whoever does not, there is no harm."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 448