From Sahih Muslim (Hadith 774):
Abdullah b. Ja'far reported:The Messenger of Allah (ﷺ) one day made me mount behind him and he confided to me something secret which I would not disclose to anybody; and the Messenger of Allah (ﷺ) liked the concealment provided by a lofty place or cluster of dates (while answering the call of nature), Ibn Asma' said in his narration: It implied an enclosure of the date-trees
Reference: Muslim 774