It was the practice of the Prophet (peace and blessings be upon him):
"When relieving himself, he (peace and blessings be upon him) most preferred to screen himself behind a mound or a cluster of date palms."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4631
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[حم م د هـ] عن عبد الله بن جعفر. مختصر مسلم ١٠٧.